Whether you're writing for adults, teens, tweens or kids, you need to develop strong characters. This isn't the easiest thing to do, especially if all you have is a morsel. That's usually how I start. I have some vague idea of what I want my character to face, what challenge I want them to overcome, but the rest...well, it develops while I write the story. This works some times, but not always, and frankly, I'd much rather have a clear idea of my character before writing the story.
So I'm working on that and in order to start improving, I came across a fun exercise. Interview your character. Seriously, pretend you're a news caster and start asking your character questions. Get personal. Go deep. See what your character has to say for him or herself.
Another fun way to develop your character is with a picture. I did this back in the day when I was writing romance novels for fun. I cut out a picture from a magazine of a celebrity or model and pasted it on a note card. Then, whenever I got stuck with character development, I would look back at the note card. Sometimes, just seeing an image of what I want that person to be like helped get the creative juices flowing.
Have fun with your character development!