Does anyone know what I could put in my sons room that would kill a mouse and be safe for my son to be around?

You need a live trap, I couldn't find a good link but if you call around in your area I'm sure you can find one. Basically, you put bait in it and the mouse enters and is trapped. From there you can release them outside.

There's no poison involved so it won't be risky for your son. They use this kind of thing in restaurants (gross, I know). Also, make sure you take a close look at your house and seal off any places that mice could enter through.

Get a box trap at the hardware store. It's a one-way trip for the mouse w/o poisons or spring traps.

A cat.