what do i need to put under my kiddie pool (389gl) to keep the yard from smelling bad?

If it is just a kiddie pool you need to empty it daily. The only thing you can do to keep from killing the grass and having the bad odor is to remove the grass. The weight from the water and the heat (especially over a few days) is what is causing the odor and grass damage. But if you are going to remove the grass and keep the pool up for several days at a time you probably need to start adding chemicals to the water. It's much more economical to empty it. Also you might put it up in a different place every day. GOOD LUCK!