My little lad is three-and-a-half now. He hasn't has a ride longer than about 10miles yet on the tandem in the photo because of the winter weather, however he his been on many 35-40 mile rides in a Co-pilot child seat. He loves it and wants to go everywhere by bike, hopefully this will continue.
My daughter, now 11 enjoys being on the tandem too, for the last three year she and I have been touring and camping by tandem during the summer, only 2 or 3 night trips but its a great adventure. My little lad wants to go camping now too so I'll probably just take him out for a one night trip to begin with.
My daughter finds longer rides no problem at all, she's done 3 100Km audax rides.
I might have to look for a new tandem soon to replace the Dawes. My wife is using it now but its a bit too big for her, she can cope on it now because of the fact that the stoker bars are not fitted but once little Joe is ready to lose the cage an use normal stoker bars the pilots saddle will be to high for her. I think I'll be looking for a second hand tandem to replace it and aim to break even when selling the Dawes.