I honestly think I would be contacting the police to talk about the issue and whether they should be getting involved. While it is unlikely they’d prosecute - esp if no images are found- around here they do get involved with even consensual “sexting” cases to really impress on kids how serious the issue is. It’s DA discretion here but could be charged as possession of child pornography if they choose to. And older kids taking pics of a younger child in the bathroom is a big deal and I’m shocked the school isn’t taking it more seriously.