I'm far from fluent, but in school the teachers used to say "
Ná bí dána!", to say "Don't be bold!" to one person, and "
Ná bígí dána!", to more than one person. A literal translation of "behave yourselves" might be different, but if you're looking for the phrase that an average Irish person is most likely to understand, I think this is it.
"Boys" is "
buachaillí". Putting it together, I guess it's "
Ná bígí dána a bhuachaillí!", for "Don't [yous] be bold, boys!" Or I guess it could also be said "
A bhuachaillí, ná bígí dána!", for "Boys, don't [yous] be bold!".
But I don't remember them saying "
a bhuachaillí". It was usually just "
Ná bígí dána anois!" (Don't [yous] be bold now!).
But hey, I'm not fluent at all, just thought I'd give it a go because this is the first translation request which looked like I might have a chance at knowing it

I hope someone else replies!
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