1. Find a resort or cruise line with a great kids'club. The kids have a great time meeting other kids and enjoying great new activities. Parents enjoy having a little alone time during the vacation.
2. Agree that each parent will get do one activity alone for a certain amount of time - schedule a massage, take a 3 hour excursion, take out a kayak.
3. Go with the flow - If everyone is exhausted, sleep in. Yes, it may seem like you are "wasting" vacation by sleeping, but that's better than epic melt downs by both parents and kids.