" Arrête de hurler! "
You tell the customer nicely to please stop yelling and use an indoor voice.
Stop it! is 'arrête !' or 'arrête ça !' in French.
s'arrêter - un arrêt
Stop misbehaving.
a bus stop is 'un arrêt de bus' in French.
yelling at the dog
yell back at them
don't upset her
arrêtez-le
Don't stop is "n'arrête pas / ne t'arrête pas" in French.
The number one way to stop a child from yelling is to not give in to their request, whether they want something or are just in a bad mood. Giving in to what they want will only reinforce the child's feelings that yelling will get them what they want.
'arête !' or 'arrête ça !'