[gerbilly]

Do you actually think the kids don't know where they screwed up their parts?

And even if they didn't know, right after the show isn't the time to mention mistakes.

It's hard enough to get up in front of people to speak, much less perform, so I think the situation you describe, if followed later by a discussion on what to improve and work on, is entirely appropriate.

Did you know that Steve Jones, the guitarist from the sex pistols, had to have another guitarist play behind a curtain for him for the first few shows? It didn't stop the band from changing popular music, and it didn't stop him from developing a very tight technique.[1]

[1] https://www.youtube.com/watch?v=XbSGR846nAg