I think criticism of children should be off limits. Us adults should be able to handle it and it kinda go's with the territory of being a high ranking martial artist. But criticize my kids (justified or not) and we may have to have a talk.
Hmm, since the kids are the product....
There is criticizing and there is CRITICIZING.
Saying a person (regardless of age) is not so good because of xyc, that's not bad. Saying a person just SUXS is not very helpful.
But your kids will be critiqued when they leave your school and perform what you taught them, be it youtube or tournament.