Welcome to bringing order to your creativity! Like a conductor standing in front of an orchestra, you can find places for all the voices you’ve mastered. And like a conductor you can bring forth each one for their solo time.
If your kids have a bunch of stuffed animals or toys you can begin there. If not, but you are more artistic and creative anyway, you can draw pictures of what you think your voices look like. Big low voices, as I’ve mentioned before, can go with big lumbering giants or you can give them a tiny mice-type voice to mix it up just for fun.
Now voices are one thing, but developing a character, a personality, for them is a step further in. What kind of a giant is it: nice, angry, silly? Having that solidified directs much of the story you’re creating as they face different situations.
For example, my son has a fox he loves more than anything else. His fox has a flexible body that can move its legs expressively. So I made him into an exasperated little character that whenever he gets asked a question, no matter how easy, gets overwhelmed while trying to answer and flips over onto his back with a great sigh of exhaustion. His legs flop out to each side when I flip him over which accentuates his exasperation. This gets my kids laughing every time.
WARNING: If you are dealing with a favorite toy of your kids, it is imperative that they approve who you are making them to be.
Developing characters adds a more concrete world as you tell stories with your kids. It happens automatically when you tell family stories. They already exist with all their peculiarities. In the world you create with your kids, give it people that can walk there and interact with it. Like in Genesis, God made Adam and Eve to walk the world He made.
What will your Adam and Eve look like, who will they be, who will they become?