I have some vids, but here is the most recent of my daughter on a JR50. She's nine and just a bit too big for the 50.
As a next step bike, look at the XR/CRF70, TTR90, or KLX110. I think that 70 is smallest, but not by much over the TTR90. The KLX is maybe .5" taller than the TTR90. I think they are all close enough for a next step from the 50.
