Just a little trick that worked for us that I wanted to share.
Now that Little Ms. E is about to turn 5, she is easy to talk with, ration with and include in making plans. The night before we flew to Philly we had a talk. I told her that I was going to need her to be a big girl and help mum and dad with Harper, seen as she is only 2, and that sitting still for 5hrs was going to be hard for her. Ms. E was excited to be included and help keep little sister happy and occupied during the flight!
I explained that while traveling was an exciting adventure and fun, there may be some times where we all get a little tired & grumpy so I suggested that we have a "safe word." Something that if her or I were getting grumpy and not being so nice, we could say this word and it would snap us out of it and remind us that this was an adventure, that we loved each other and to relax and laugh!!
She picked "CHICKEN PANTS"
Like A Charm