Even though mine and my siblings kids are still only little, we were talking about this recently. My sister and brother both have great inlaws who would be happy to help out but we also discussed spliting the holidays between the three families and each having some days off too. We figure between the six adults it would be the easiest way and then the cousins all get to play together too. It would be a headache for the parent "on duty to deal with 6 or 7 children in one go but it's not like it would be a week straight.