What do you consider less than ideal?
You said they'd be allowed to keep the toys at their home, for the kids to play with there . . . which seems to imply two things -- 1. You're okay with the kids playing with the toys SOMEWHERE, just not at your house and 2. The kids will actually want to play with them. Why not just let them play with them at home, be appreciative for the gift, and get on with your life?
I have a really hard time thinking of things that my kids would hate/not use at all. There are a few characters they REALLY don't like, so yeah, it would suck to get a gift that was character-themed (however, when this happened to my daughter she was exceptionally gracious all on her own
-- and then gave the movie to a friend's daughter, who loved it). Beyond that, unless they're being given things that are way below their age levels or things that aren't toys at all, I'm finding it hard to believe that someone could even come up with years worth of inappropriate toys.
Now, maybe I should end this by saying that I'm not picky about toys. My kids have a whole range from plastic crap (some of which they really wanted and really enjoy) to expensive Playmobil and beautiful wooden things, etc (same). Sure, I have preferences -- I'd rather spend my money on nice things that will last . . . but I'm not going to deny them other things that give them a lot of pleasure.