Transcript for Dad warns of privacy risk for kids in Musical.ly app

Back with a new alert on popular apps that could put your children in danger. A father warning parents after he discovered his 7-year-old was receiving very disturbing messages. ABC's Mara schiavocampo is here with more on this. Good morning, Mara. Reporter: Good morning. We all try to be vigilant about what her children are doing but a lot of parents have no idea that there are messaging features in apps that are insanely popular with kids like musical.ly potentially allowing strangers to contact your child directly. This morning, a father speaking out after his 7-year-old daughter told him she was getting disturbing messages while playing on his phone. We never thought in a million years that we would receive anything other than family fun. The account was just at the default settings. We weren't aware of any public or private settings. Reporter: Brad says mad San was using musical.ly creating music videos to some of their favorite songs when someone allegedly posing as a child began contacting her through the messaging function of the app asking her to send photos of herself without a t-shirt on calling it a secret between us only. She had came to us and let us know that there was some -- someone averaging her to remove clothing for pictures and she knew it wasn't right. Reporter: He posted it on Facebook as a warning to other parents and filed a contemplate with the local police department. It could be another young child on the end of this conversation or it could be an adult. If they believe it is another kid they would share home information, person ago information about themselves. Reporter: Musical.ly just one of many recreational apps featuring a messaging option. A mom in Louisiana says she believes her 8-year-old son was contacted by a sexual predator while using roblox and reported it to police. Now, roblox released this video. Keeping our community safe is our top priority. Reporter: Some of the protections include in-game chat filtering restricting a greater words of words and phrases and parental controls that enables parents to shut off chat capabilities all together. Musical.ly outlines theirs on their website advising parents to use the private account setting and enable the only friends option for direct contacts. My message to parents would be to pay attention. I'm glad it didn't go further. We would be having a different conversation right now. Reporter: Now, musical.ly also notes their app is for kids 13 and older and, again, you can change the privacy settings to limit who can contact you but, Amy, the issue is a lot of parents don't realize there is a messaging feature so it's not the thing they're looking out for. Information is power. Joining us from Seattle is Callahan Walsh, he is a child advocate with the national center for missing & exploited children. Thanks for being here. This literally happened in my family a few years ago. My kids were on a cooking app and were talking to each other. Someone posing as someone who was there for an anti-bullying campaign started messaging them. I saw them and they were inappropriate. This can happen in almost any app for children, correct? That's right. You know, a lot of these apps are changing their features and some of those features are including this peer-to-peer communication where as you said strangers can talk to your children unbeknownst to you. The best way we tell parents is know the technology. And the best way to do that is to get on these apps with your kids, figure out how the features work and make sure it's right for your child. It's a shocking thing when you see all of a sudden your child messaging someone and don't have a phone like who are you talking to. There are parental controls. Talk about how those work. Well, we definitely recommend for parents to use the parental controls and many of these platforms do have them. They don't want this exploitation to happen on their networks, you know, the internet has changed life for the better and so many different ways but it's also created new ways to exploit children and those parental controls are there for parents to be able to make sure their kids are staying staph on these apps. Callahan, obviously kids are downloading new apps every day so you might not have a chance to go in for those parental controls when they're downloading these. What do you say to your children? What's the conversation that needs to happen? Well, there's plenty of tips we give to parents but first the setting of ground rues and sticking to them. Also having ongoing conversations with your kids about safety. You want to empower them to make safe and smart decisions on their own and also look for teachable moments. Something concerning pops up use that to empower your children. Teach them how to stay safe. The national center for missing & exploited children has great education programs, netsmarts, in fact, a great way to teach kids to be safe online. And parents have to teach themselves first, Callahan, thanks. We appreciate it.

This transcript has been automatically generated and may not be 100% accurate.