That's a lot like adapting a play for the specific needs of your cast. Children are always growing up and moving on, and younger children eagerly appear wanting a chance. Being a director of Children's Theater is a lot like gambling. You cannot know how the dice will roll. You can only guess at how to cast the show because many of the young children don't even know how to show you what talents they posses. Many talents develop right before your very eyes.
So, you need to be FLEXIBLE. It's best to use material that has built in ways to adapt it to fit the needs of the children. Lead characters who can be either male or female, old or young, tall or short, etc. Secondary comedic characters who are well-drawn already, but leave room for improvisation to make them more memorable. Lots of singing and dancing that can involve everybody equally (regardless of ability). Also, the possibility of completely eliminating characters that you just may not have enough actors to fill.
I like owning all of the rights to a show. That way, if I need to completely rewrite the script, add another character or group of characters, give them a new song, etc., I can.
Once I went home from rehearsal the first day realizing we needed a new song. My music leader suggested a new Opener to bring on the cast. So, in a flash of inspiration, "Over Yonder" became the opening production number to "Stone Soup."
When we did "A Successor to the Throne" at an Elementary School (4-6th graders), a group of talented older girls needed bigger parts. So, they got a revamped scene and a reworked song, "Autumn Lingers on the Breeze."
Because we had a very talented singer in the cast for "Momotaro" and the character she needed to be didn't have a song, I went home and quickly wrote one for her. "Hero" actually became a nice theme song for that show.
Then, just last summer, the Fox in "The Tale of Chicken Licken" needed a beefed up part and a new song, "You Oughta Keep and Open Mind."
Who knows what will be needed for this summer's Theater Camp?