I take it back

Last week I posted about pants patches for my little guy. Yes, they were easy to do. Apparently they are easy to undo as well. Every patched pair of pants had become un-patched by day's end, so now I need help. I will have to break out a needle and thread and patch them by hand. (no, I don't have a sewing machine). Who knows about sewing? What kind of material should I get? What should I do? Any and all tips appreciated!