Tweens and teens have always craved time with their friends. But with a smartphone in hand, their communication keeps changing. Instead of talking, they text. Instead of texting, they send an emoji. And now, with apps designed for social video-chatting and live video-streaming, kids don't have to settle for sending static images and words. They can watch, create, and share video -- preferably live video . Not only is it authentic and spontaneous, but it's also the closest thing to hanging out in person .

So, what are these apps that are taking kids by storm? Live video-streaming is like live TV. Users simply fire up an app such as Facebook or Periscope, turn on the live-streaming feature, aim the camera on themselves, and broadcast to whomever is following them on the app. Social video-chatting is similar to video-chat apps such as FaceTime or Skype, but it's usually done with lots of people.

While these apps tap into teens' natural desire to connect, relate, and belong, there are some modern-day motivations and concerns, such as chasing fame, oversharing, and even criminal behavior, that parents need to be aware of and help kids manage. Teens have used the technology to stream their own suicides or crimes , so it's very possible to see horrifying things because live video is so difficult to moderate. Live streaming even has its own unique culture. Just as people have become famous on YouTube, there are live-stream celebrities , and kids tune in to watch them, follow them, and even buy them "gifts," which are basically online donations. In other words, kids are making money and getting famous just by hosting live streams of themselves. Hollywood celebrities and politicians are even in on the trend, and live streams can be a great source of on-the-spot news and real-time participation in important events

If you want to learn more about social media in general, you can also check out other popular social media titles and their important features to get a sense of what else your kid is using. Here are the most popular social video-chatting and live-streaming apps and tips on what parents need to know.

Social Video-Chatting Apps

Snapchat. Aside from all the other features kids love, this mega-popular app also offers video chat. So far, it's only possible with one other person, but group chat can't be far behind. If users want to use video chat, they contact a friend and start the video stream. The friend can either watch or join and doesn't have to be visible.

What parents need to know

Though for many parents, Snapchat feels like the most impenetrable app out there because there's no feed to check and messages aren't stored, it's actually somewhat contained.

Instead of broadcasting to random strangers, teens can use the video feature with real friends or -- if they've been too friendly in sharing their handles -- ignore calls from those they don't know.

Encourage kids to use Snapchat's built-in privacy settings.

Houseparty -- Group Video Chat. Instead of hanging out at someone's house after school, teens can go into their rooms, close the door, and hang out on their phones. Up to eight people can be on a call at once, and groups can lock their chats so others can't join. If a friend of a friend joins, users get a notification, which lets them jump off the call if they want.

What parents need to know

The biggest risks with an app like this are not things like predators or mature content. Instead, it's kids being constantly connected and trying to multitask while chatting.

There's also a risk of kids using it at odd hours, such as when they should be sleeping.

Set limits around device use in general so kids know when and where it's OK to use devices.

AirTime -- Group Video Chat. Not only can you have a live video chat with your friends, but you also can easily search for and share videos and music right from the app. Through settings, teens have control over access to the "rooms" they create, keeping them totally private, requiring access requests, or limiting access to friends of friends. Because users can search for content on sites such as YouTube, they can potentially encounter all manner of content.

What parents need to know

There's no mystery why teens love AirTime, since sharing music and funny videos in real time is really fun.

To keep out random people, parents might want to go through the settings on each room kids create so they're aware of who's able to access each one.

As with all the other apps, multitasking and sharing content can get kids into trouble, and mature content is only a click away, so make sure your kid knows how to use this app safely and responsibly.

Live-Streaming Apps

Facebook, Instagram, and YouTube Live. These giants have all kinds of bells and whistles, and all of them have jumped on the live-streaming bandwagon. All feature the ability to broadcast live to followers, although there's very limited interactivity: Those watching can "like" and comment, but it's not really a two-way street. So, instead of just posting a picture or status update, teens can "go live" and people can access their video in real time or later on.

What parents need to know

As with all live-streaming apps, privacy and safety are major concerns.

Since kids are often motivated to broadcast themselves to get approval, they may share personal information when asked or do things they wouldn't otherwise.

In terms of viewing, live streams are extremely difficult to moderate and control, so upsetting, racy, or otherwise iffy content can easily come through.

Talk with your kids and set expectations around creating and watching. Also, go through your kid's settings with them and make sure only friends have access.

Periscope. One of the first video streamers, this app is owned by Twitter and allows you to post live video directly to the site. Though Twitter isn't the hottest platform for teens, and they don't spend a ton of time on it, they do use it. Though you can send "protected" tweets, Twitter is really a public forum, so most people are posting to everyone.

What parents need to know

As with other live broadcasts with no delay, the main concerns are what kids might see or what they might do during a stream.

Though many videos are related to politics or celebrity promos, criminal activity and violence do occasionally show up.

Before they jump in, discuss the possibility that kids could see disturbing videos.

Live.ly -- live video streaming. Created by the developers who brought us musical.ly, this video-sharing tool is like many others in that kids stream video to their friends and followers who can comment and "like" to interact with the broadcaster. Because of musical.ly's popularity, live.ly has a built-in audience that bounces between the platforms, but livel.ly is less about performance and more about hanging out.

What parents need to know

Other than what a kid might see, the biggest risk here is oversharing.

Since users are often broadcasting from their homes -- and even bedrooms -- they're comfortable in their own spaces, staring into a tiny camera. When viewers ask for a Snapchat handle or phone number, kids often oblige without knowing who's doing the asking.

Talk about what not to do or share, even if someone asks.

Take a spin through some videos to see what people are streaming, even if it gives you the creeps.

YouNow -- Broadcast, Chat, and Watch Live Video. A very popular gathering place for kids, this app has its own celebrities and culture. Not only can you comment and like someone's video, but you also can buy gold bars and other gifts, which generates money for the broadcaster. For the most part, there is very little mature content, including swearing, partly because users do get blocked and banned -- frequently. Though they don't promise to filter out all iffy stuff, there is A very popular gathering place for kids, this app has its own celebrities and culture. Not only can you comment and like someone's video, but you also can buy gold bars and other gifts, which generates money for the broadcaster. For the most part, there is very little mature content, including swearing, partly because users do get blocked and banned -- frequently. Though they don't promise to filter out all iffy stuff, there is a whole set of instructions on their site letting kids know how they can get blocked and how to block viewers.

What parents need to know

Though all the risks that exist with live video still apply here, YouNow seems to have a bit more oversight and follow-through with noncompliant users.

Kids still share personal information, and they're still broadcasting from personal spaces.

It's important for parents to talk to kids about spending real money, since it's possible for them to shell out a lot of real cash.

If your kid is itching to get famous, discuss the risks and pressure that come along with that ride.

Hype -- Interactive Live Video. From the creators of the now Twitter-owned Vine app, this broadcasting tool has a lot of fancy features and has retained some of Vine's popular posters. Being able to add music, images, and video to your streams definitely adds interest and production value, which sets this app apart from the sea of kids sitting on their beds, staring at the comment feed.

What parents need to know

Though the risks and concerns with this app are very much the same as those with other live-streaming tools, the other potential pitfall is that if a user logs in with a Facebook account, the Facebook profile name will appear, which is often someone's full name.

If your kid is going to use Hype, have them create a unique login name instead of using an existing account.

Join the conversation See the latest news and share your comments with CNN Health on Facebook and Twitter.

Live.me -- Live Video Streaming App! Broadcast, Chat, Share, Follow and be a Star!. Like the others, this app is a one-way window-style streamer, where users broadcast to unseen followers. Live.me's overall culture is more mature than some others. During our review, we saw lots of bad behavior, from racial slurs to kids being asked to take off clothing.

What parents need to know