That is a Storeria Dekayi, Dekayi brown snake, and a very pregnant one at that.
She is absolutely harmless.
When she has the babies (born live) they will be this tiny, and very difficult to feed.
So the best thing you can do for her is to release her exactly where you found her.
They make great pet snakes, will eat cut up night crawlers (worms) and have sweet temperaments.
If she was not pregnant, I would suggest keeping her as a pet for your little one, but they have big litters, up to 30 babies at once.