So how do you do that?
Start by re-introducing yourself to your long-ago friend. Sure you knew this kid twenty-five years ago, but that’s a long time. Remember, if you’re writing in the time-frame of your own childhood, that would be an historical novel. Maybe you wore neon orange and lime-green parachute pants as a kid, but make sure your characters dress the way kids do now.
And notice how confident elementary school children are today. They’ll say anything to anybody. Even to grown-ups (with whom they’ll be on a first-name basis). These kids tend to have a better idea of what they like—and don’t like—and they’re not shy about letting you know.
Today’s boys and girls are more likely to be best friends with each other than they were back then. They’re tech savvy, and they’re less likely to be playing jump-rope or monkeying around on jungle gyms.
And in what appears to be an evolution of consciousness, the children of today are more comfortable with talking about how they feel.
Character development: let your characters speak for themselves
Here are three ways you can handle that:
1) You spell it out for your reader:
Jason hung back. He wasn’t a very good swimmer, and he always felt embarrassed when he thrashed his way across the pool.
2) Jason tells them, but in case your reader misses it, you tell them, too:
“Hey, Jason! Come on in!”
“I can’t. I forgot my towel.” Jason had hoped that no one would notice that he wasn’t swimming.
3) Let JASON show your readers how unsure he is:
Sam and Eddie dove into the deep end. The water was a shade darker—and colder, Jason thought—when the drain was so far down you could hardly see it. He grabbed a kickboard from the deck and jumped in.
"Look! I'm Eddie! I'm a big baby!" Jason held his nose with two fingers and began splashing his way across the pool. The spastic sound of his feet slapping the water trailed behind him, but all he cared about was the clock on the wall over the picnic tables. Two more minutes, and the lifeguard would blow the whistle for adult swim.
Character development: be consistent
While there might be one quirky character in a book, they can’t all be. The others need to be something different to provide contrast.
Mostly because that’s how it is in real life. Everybody’s different. And in order to create a scenario that your readers can get lost in, they need to feel the way they do when they meet real people—interested, curious and wanting to know more.