My FH has two boys 13 and 11, we wouldn't consider them not going with us. However it does make it easier that they are a little older. Actually I find the biggest benefit of choosing a DW is the boys are as excited as we are, and they've actually been interested in some of the wedding decisions. (I'm working on them to do a little speech for their dad).
They are going down with us, but we're staying 2 weeks and they're going to have to come home with my family. We've travelled with them lots before, and never been asked for any paperwork, but always figure it's better to be on the safe side, especially since my parents last names are different, as far as we know we'll need to get a notarized letter, with permission from their mom. Luckily we're on good terms so that won't be a problem