It would appear they have probable cause.
I’d have a beef with a search warrant of the phones too. I think they would need to show that the phones have evidence of a crime, or were used in the commission of a crime, and BTW what crime do they think happened anyway, etc.
That said, I’ll bet a day’s pay that we eventually see a picture of one of the “youths” with a big smile on his face poking a stick between the bars, or somesuch.