Well, JF certainly doesn't know for sure

Both the skating pictures strike me as generic "Hollywood kids at play" poses; both the other girl and the boy seem uber-familiar as child performers of that era -- although the boy is definitely not Ronald
Thoroughbreds Don't Cry Sinclair. One of the Judy books or magazines features a photo of a boy adjusting Judy's skates for her; I can't access that publication right now, but it may well be from the same event and give indication of the actor's name.
Meanwhile, my other guess is that the Judy/Mickey gallery shot was taken the day she participated in that charity tennis match with Paulette Goddard, Bill Tilden, and others. The outfit seems to be the same, yes? (Again, I'm not where I can investigate this further; sorry!) I think the blond behind them may be Mickey's buddy and sometime stand-in, Dick Paxton.
How's THAT for massively inconclusive?!
