[cdeweese]

Do they know not to do it? I would make them donate (or you return the ones they opened) if they know better. I would allow them to have other gifts, but not the ones they opened.

Edit: Especially since they they were being sneaky about it. Telling them they aren't getting them and then giving them those gifts later ruins your credibility as a parent. They would absolutely lose those gifts and not get them back.