In the do-re-mi sequence at the very end the children and Maria are jumping steps singing. Liesel and Louisa are supposed to be coordinated with each other, but Louisa gets very confused with what step she's supposed to be on and keeps looking over at Liesel to get back on track. It's pretty funny to watch!
This might be a mistake, but I suspect it's deliberate, since most kids putting on a performance like this often do that in real life. I see it myself at home all the time. I think it makes it more realistic