These videos are taken from the end of our almost 1-hr session; in the beginning, E was frustrated because she kept losing her footing on the pedals. (Biking without her feet strapped to the pedals is relatively new for her).
It's not evident from these videos but Vivian also had trouble with the bike at first. Both Viv and E are quick learners--but obviously Viv has an easier time with this sort of thing. By the end of of our time, Viv was biking well (but pretty tired, she said her legs hurt) and E had made significant progress. I think it will be much more difficult for Elena to feel where her feet are while wearing braces...we are considering putting adult-sized pedals on her kid-sized bike.