Oh no! If he is that small and in the "flea stage" (where they jump a lot), then I understand your concern, cuz this could be a very difficult task!!!
I have always heard (and I think I have heard here as well, in previous posts!

) that a good technique is to put a bucket on the floor, standing normally, that is too deep for a mouse to jump out...and then put something yummy in it, and stack some books going up the side of it on the outside so that he can get in, but won't be able to get out.
Other than that, you may just have to go out and buy a humane trap from a department store type deal...I think there is a brand called Have A Heart???
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-Tare

"Heaven goes by favour. If it went by merit, you would stay out and your dog would go in."
Proud mom to Halle (dog), Sugar (cat), Tiffany (beta fish), Mango (molly fish), and Macy, Paris, Tessa, & Ruthie (mice).
RIP Kiska... the greatest...