Would these kids appreciate something like that? I'd hate for you to waste your money. It really depends on what interests the kids and how they are being raised. Are they raised on video games? TV? If so, then it's going to be pretty darn hard to find something they will actually check out. If you are giving the parents liberty stuff this makes me think that they aren't really awake either? It may make a better impression on the parents, if you give them the Liberty stuff and then get their kids just a normal toy. It would make you seem like a good person, thinking of a unique gift for them but then also getting something the kids would enjoy.
If I gave my spoiled, ungrateful cousins something like a silver dollar or a book about the Constitution, they would literally go "oh...this is stupid" and then go back and play with the other toys. Their parents are typical TV watching Americans and they raised their kids the same way. It's impossible to get through to them, so I stopped giving them gifts after this happened 2 years in a row.
Maybe this isn't what you wanted to hear, but I just figured I'd give you my perspective on things from my own experience with this.