"No, thanks, boys."
Maybe just a programming blip. If they meant male kids, Jungen would be right. Jungs means "boys" as in buddies or chaps or lads. Note, I am not a native speaker though.
So if you wanted to say the sentence and you were talking to "male kids", would you still say "Jungs"? Or would you say the sentence another way?
I agree with christian. As the tone of the phrase is rather colloquial 'Jungen' sounds a bit strange. Yes, sure: you can use 'Jungs' to refer to a group of boys. Die Zeichensetzung ist auch ziemlich fragwürdig...
After a second thought: I guess 'Jungen' doesn't work because the sentence is a direct address. It sounds very aloof if you directly address a group of boys as 'Jungen'. If you speak about a group of boys, 'Jungen' is generally preferable. I'd say 'Die Jungen gehen spielen' but always 'Jungs, geht mal spielen!'.