I have been giving this some thought as well and i am quite suprised as to your reason DT for not wanting your kids as a pillion, I must be honest and say i had never given it a thought about what they will get up to in the future regarding bikes.
I did take my little girl out on the bird she is 11 and she loved it , now she wants to go out all the time but because she hasnt got leathers (we wrapped her up real well when i took her out) I dont want to .
She was a great pillion because she weighs so little and i didnt even know that i had her on the back , so the temptation to blast it was tremendous, but i didnt, fastest was about 60 .
now I took my lad to the P&P at Tazs and he was going to get a moped next year before we went . He doesnt want one now , he wants direct access when he gets older, so he can get a bike with a bit of grunt
It is nice to have your children taking an intrest in our intrests (the XX )
and my advice is do it safely and take them on the back they will either love it or hate it , but at least it gives them a chance to find out , I think worrying about what might happen in the future is bit pointless , give em a safe pillion ride then they will hopefully recognise an idiot rider and they wont go pillion with them, and as we are all aware safe does not have to mean slow.