phnuff, I took our son up when he was 5 and our daughter just before she were 2 (with Wifey in the back next to her).
Keef, I have found exactly the same as you. Our two (son - 8 & daughter - 2 1/2) seem to treat it as about as exciting as a trip to the shops. What makes matters even worse if that our son occasionally has a bit of a tantrum in the a/c if he's ignored (ie when you're busy). I had an interesting incident a few years ago where he started yelling when I was trying to talk to Farnborough LARS during an IFR trip back from Blackpool.
I do wonder though if it will change when they get older and become responsible for their own means of getting from A to B. Hopefully...
FujiF