Tough question When I was about 10 and a half we took an 8 hour flight my mom had me put on a diaper but as I recall I slept very little so there was no wetting. I was to exited about the trip to sleep. IF there is a chance that they will fall asleep and wet then I would have them put them on to be safe. They will need something to change in to and a small bag and these days the likelihood of being searched is very high. There is the possibility of having their goodnights seen when being checked out by security. Also if security sees your child the 14 year old appear to have something unusual under her clothes it is very likely they will ask questions so be prepared. I hope you have a great time! Steph :)