My DBF and I took his daughter (8yrs) out on her mini road bike. She hangs on the sidewalk. He and I ride on the street next to her and take turns doing sprints and returning, switching off. It must be quite a sight, him on his Madone with his team race kit, me on the Colnago with my PD kit, and the little one on her itty bitty Fuji with her leopard print jersey.
Little one did 12 miles. I did 15, sprinting and returning, he did 14 the same way. Even got a few hills in. Not enough distance to really count as a ride for either of us, but she was bushed.