We also have 4 kids (3, 6, 11, and 12) and as others have said, we always pack way more than we need. Our flight to FL is 2 1/2 hours and in repeated flights we have never really had an issue with keeping kids entertained. Little ones often sleep and older ones seem to enterian themselves fine for that length of flight.
Often my kids have been entertained by something simple and enexpected.
Last year our youngest was 2 and she was entertained by a small stuffed animal...I and would tell her stories about what the stuffed animal (a moose) was going to do in Disney - she loved it!
I think a huge benefit of flying is that planes are loud, so the pressure to be quiet is removed. My kids can be perfectly entertained for 2 1/2 hours on a plane, but try and keep them entertained and quiet in church for an hour when they are under 5 and I want to tear my hair out.