Do you have a child in Scouts? I do, and I'm amazed by the amount of patches they get, I remember back in the day the patches were few and far between, now there is a patch for everything and they all need to be attached to their vest/uniform. Most of the new patches are iron on but I've found they don't stay on well so my solution was Krazy Glue, it works great, super easy to attach and they stay on!!!
When gluing put a piece of wax paper underneath and on top, then put a heavy object on top and let it dry.