Sharing is overrated.

True, personal generosity is one of the first lessons parents and teachers pass along to preschoolers. But that concept gets complicated when kids enter the digital world.

The basic rules of social media sharing may seem simple: No one wants their children posting home addresses or school names online, just like they don’t want to see pictures from a high schooler’s Friday night party.

Still, many parents appear to have a hard time guiding kids' use of the internet. Studies have consistently shown kids and teenagers use at least one social media account their parents don't know about. Research published by the Center for Cyber Safety and Education in 2015 revealed that 4 out of 10 middle schoolers admitted using the internet in ways their parents would not approve, and many kids lied about their age online.

So, now that millions of students have headed back to school this week with smartphones in their pockets and backpacks, it's the perfect time to talk with kids about what to share – and what not to share – online.

But parents shouldn't just talk to kids about digital privacy and security in the age of nonstop Snapchats and Instagram posts. They should actually demonstrate what responsible sharing looks like – which may mean resisting the urge to post every moment of your child's life on Facebook.

I took my first steps toward protecting my kids' online lives when they were 4 and 7 years old. I was working as a social media consultant at the time and decided to write a social media policy for my own family. Here’s a sample:

All conversations, activities, and events in our home shall be treated as confidential. Confidentiality may be waived by any member of the household upon explicit request. Do not post, tweet, Facebook or otherwise share any images or activities of family members without their consent. This applies to both parents and kids. We must respect the wishes of our family and friends regarding the confidentiality of our social engagements and conversations (no matter how cute they are).

At first it seemed a bit too serious, but it wasn’t long before those rules changed our entire family dynamic.

I gave each child their own pseudonym, Little Peanut and Little Sweetie, so that I could refer to them online without exposing their real names. When my five-year-old daughter asked to add her "fairy sightings" to Wikipedia, I posted a note to Facebook about Sweetie’s ingenuity. When 4-year-old Peanut said, "Mummy, if you eat this gum it will make you blog everything," I captured his joke in the form of a tweet from @LilPnut.

Initially, I kept these posts to a tight circle of friends by keeping the kids' accounts private (so I could control who read the tweets I posted in their names) and setting up a small Facebook list of people I knew well. Over time, however, I became a little more self-indulgent, and couldn’t resist sharing my stories with a wider circle: surely everyone would be interested in seeing Sweetie dressed as her own made up Halloween character, "App Girl."

(How on earth did my mother survive parenthood without sharing every moment of my childhood with an audience of thousands?)

After writing our social media policy, I started asking for permission before sharing these stories, even with my small group of online friends. The kids usually agreed. But I soon discovered the frustration of taking a fabulous photograph or having an extraordinary conversation that the kids, for whatever reason, didn’t want me to share with the world.

Now that the kids are old enough to take an interest in social media themselves, I can see the benefits of repressing my urge to share.

My 12-year-old daughter now has her own Twitter account (no, her age is not a terms of service violation), and she’s very conscious of what she shares and who is following her. Whenever someone with a creepy profile picture follows her, she blocks them and lets me know. When she sees sexist or racist comments on Minecraft, she immediately reports them to the administrators. And she recently scolded me for talking about her Twitter handle on Facebook, since that could compromise her anonymity.

Way to go, mom.

My 10-year-old son doesn’t post to Facebook or Twitter, but he and his sister make their own "Let’s Play" videos, where they narrate their Minecraft gameplay so they can post it to YouTube. If his sister accidentally uses his name when they’re recording, he insists they start over so they remain anonymous.

Still, I monitor their activity in order to avoid any issues. I noticed as soon as my daughter tweeted something with an adult-themed hashtag: Since we have her Twitter password, we were able to delete it immediately. When we talked it over, we realized she didn’t know what the hashtag meant – so now we’ve agreed that she’ll ask us before using any hashtag or terms she doesn’t know.

Cultivating that judgment isn’t just for our daughter’s protection: It’s also for the benefit of her family and friends. Teaching kids to ask for permission before they post someone's picture – or before writing about someone else – is a good foundation for ensuring they respect other people's privacy, and don’t fall into online bullying.

But it's hard to expect that kind of discretion if you've been posting your kids' photos without their permission. That’s why I encourage other families to adopt the "ask before posting" rule in their own homes, and to start talking with their kids about social media while they’re still young.

You may need to own up to past mistakes, or at least consider offering to let them review your past posts, and give your kids the option to delete or hide content they don’t want anyone to see. If they feel overexposed by what you've shared, you have a great teachable moment: Their feeling of vulnerability will give them a visceral lesson in why it's important to ask for permission before sharing.

The more we start talking about what "good sharing" looks like online, the more the internet will evolve into the kind of community we want for our children.