I agree with all Elle 's pointers about how children speak. Another thing I've noticed, especially with very young or very enthusiastic children, is repetition. Sometimes children don't have too many words to use, but in an attempt to keep going, they stutter and repeat. My sister babysits an overactive toddler, and when she talks, it sounds something like this:

And--and it was like, like this big, and there was the sun, and it was yellow and big and Mommy said don't look, but--but I...so I...

There's a lot of trailing off and starting back at the beginning. I've also noticed sudden subject changes thanks to really random associations kids make with other things...