Flying with kids- how young is too young?

I took a friend, his wife, and their 5 year old son up last spring. The
kid sat in the back seat with his mom, and he loved it.

A fogbank cut the flight short, and I've been promising them a full length
sightseeing flight since. The kid's eager to go, but his mom is probably
going to bow out.

Aside from airsickness (I took extra bags!) I was most worried about the
kid chattering constantly over the intercom, because he talked non-stop on
the car ride out to the airport. I managed to impress the importance of
being quiet most of the time on him, though, and he was fine. Even asked
several times if it was OK to talk then...

(Along with 'no walking on the apron without holding an adult's hand',
because I could just picture him dashing off into another Cessna's
prop...)

I also took another friend & his 8 & 11 yr old kids up, and that was great
too. I've had more trouble from a few adult pax than the kids!

Brian.