Just as a suggestion, I would probably next time state that on the invites then if that's what you are really hoping for. Since my first kids birthday, if they are having a party, I will state on the bottom of the invites....(if you would like to purchase a gift please consider books) or (if you would like to purchase a gift please consider gift cards) ( if you would like to purchase a gift please consider cars).....these are just examples that I have done & I just did it for my kids birthday the other day & put gift cards. I do that for that reason of not wanting a lot of toys, the same stuff or clutter. I am trying to get my kids to really think about the stuff they purchase & be smart about it. It helps them with learning to manage their '$' and they love going & shopping with their gift. I know that's not what your question was, but thought I would just share this tip for you. My hubby had a problem w/it when I started doing that 11 years ago, but it has worked out since that is not "traditional". When they are younger, I always ask for books. Also, I put "if you would like to" because there have been times that a few of my kids friends didn't show up to a party because they couldn't afford a present. When I found out about that, I was hurt & felt bad that happened, because for us it's not about the presents, but about the memories they are having w/my kids. I don't ever want someone to feel & I am trying to teach my kids that it is not about the gifts but the friends. I also ask them, if someone couldn't come to their party because they couldn't buy a gift for them, how would that make them feel & what to them is most important. Don't get me wrong, I love presents, but I don't want that to be the emphasis or the determining factor of a kid not enjoying time w/others because of that.
As far as taking back, you would probably just have to go & see what stores they may have been purchased & just get an in-store credit if they allow.