The longest training ride we did in preparing was 74km. I found any distance up to that was fine as long as there was one stop for a bakery! Our family all runs on bakeries!

And she was happy to ride up to 35ish km on her own bike as long as it wasn't too hilly.
The first day of the tour was 57km and she was absolutely toast by bedtime due to the savage headwind. The second day was 94km and she was an absolute trooper after I discovered giving her some gatorade just after lunch!
She did very well as my little stoker and is very keen to go again this year. We start training for it shortly and she has already been out on her own bike doing distances up to 25km or so with a friend and his daughter who is 12yo. The nice thing is this year's route is much faltter than last year's so we should have enough energy at the end of the day to socialise instead of just sleeping!
But all 11yo kids are different. The Princess has always loved riding her bikes. But one of her best friends has always disliked riding bikes, despite the rest of her family being bike-mad! Last weekend we did a nice gentle family ride of only 14km with their family and one other, and she was whinging by the time we made it to the 5km mark! So I guess there is no "normal" for kids on bikes!
