L.L.
I really don't think you can make snaps stronger. My idea is that if they keep popping open, the article of clothing is too small for the person wearing them. I am very sorry...I know what a bummer it is to have a super cute piece of clothing and not have it work/function/fit like you want it to. I bought a sweatshirt for my youngest last year for Christmas that was SUPER cute, and I bought it 2 sizes bigger than she was wearing to get use out of it...and it shrunk so bad she only got to wear it for a few months. :( Paid too much for it, too.