Imho:

These words need no attention at all:
A) Замолчи! (Stop talking)
A) Довольно!
A) Слушайте внимательно.
A) Слушайте!
A) Молчать!
A) Молчи!
A) Молчите!
All of them are usual every-day speech. Some level of rudeness can be applied by intonation and situation though.


B) Заткнись
B) закрой свой рот
These are 'B's in my opinion, but child has to be real annoying pain in the ass.
A) Закрой варежку!
It's soften version of "закрой свой рот". It's not polite if child didn't deserve it, but it's more polite than (B) in case of annoying child. Also can be said jokinly.
A) Попридержи язык!
Same as above - polite word for 'problem child', not appropriate for normal discussion.