I've been thinking about this a lot lately bc our summer trip has us flying around the globe in different patterns/flights amongst our family of 5 (our kids are 14-23): 2 parents + kid #3 TATL; kid #2 TATL; 2 parents + kid #3 EUR; kid #1 EUR; 2 parents + kids #1 and #3 EUR. Then we all hook up and travel onwards together. The last flight before we meet up is one where 4 of us would be on one flight and #2 kid would not be. The thought of one kid being left alone should something happen to the rest of us is too much for me. So I'm booking one parent and one kid on two separate flights for that. It's a little puddle jumper 1 hour flight with 2 leaving within 30 minutes of each other. I think that's where I just have to separate us: when it's 4 but not the 5th.