That could be. But I am not a kid, and I have never heard or read that phrase in all my life. So it must be pretty obscure in this day and age.
You’ve never heard anyone say ‘you lot’?
I’ve never heard anyone say ‘youse’, unless it was in a movie, or my husband was making fun of people he heard using it in his youth. But I understand that it’s quite common in some areas of the US.
Y’all take care, now.
But obviously you are not only poorly educated but also not well read, nor culturally astute.
I bet that there are many things, which are unknown/obscure to you, but which millions of others know about.