For a 7 hour trip, that is a long time without charging.
From what I have seen of battery life benchmarks when watching movies, Apple iPads traditionally outlast other devices by sometimes by a couple of hours - literally.
If you are 5 hours into your trip and the device dies, that might not fare well for the remaining 2 hours. Or, if you have to wait 2 hours before your kids can start using their devices to ensure they have enough battery may not be what is needed either.
You need to balance that with the cost however obviously as Apple products will be pricier.
Just some thoughts.