If you for example live in Alaska, taking your children at any age flying isn't even a question. It's just normal. You are not the first, with this problem.
If the child is in a good car seat, it can not open the restraint. It is designed like that. But there aren't many planes with isofix (none as far as I know).
As it is with adults, some kids like it, some could not care less, some hate it. At my first flight as the proud helicopter pilot dad, one slept, the other needed to go after half an hour. As long as they don't hate it, you'r good.
Therefore, going flying with the kids should just be normal. Who knows, one day, your daughter asks for the hangar key, instead the car key, and then you will be happy ...
Here is some information that might help:
http://thefamilyairplane.com/aviatio...sets-for-kids/