Easy and cheap solution

They work good for what they are supposed to be for but make sure the material to be clipped is pretty thin. They won't pop open (that I've seen) but can be tough to close, especially for kids.

The dollar store bag clips work pretty well for most bags I need to keep closed.
I find if the bag is still quite full that the clip can be difficult to clip. Sometimes I prefer
to use a claw style clip to avoid losing the clip.