There are a few different issues here.
#1 - IF, and I say IF, the parents aren't interested in owning firearms, of shouldering that extra responsibility, that is entirely their right. Hence, if the kid goes about and aqquires some guns, be it totally illegally buying them off the street, or equally illegally, but probably more common, has his 21 year old buddy buy them for him, then yes, if the parents are behind throwing the book at the kid to teach him a lesson, great.
#2 - However, if as others have stated, if these are the legally owned guns of the parent, even if they were bought for the kid (and my parents did teh same thing, bought me a ruger 10/22 that was 'my very own') then there is absolutely nothing wrong with that picture. Hell, if they belong to a friend, and he went out shooting with that friend and friend's parents, took some pics, that is plenty okay too.
Further, someone mentioned "Sounds like the kid doesn't need to be around firearms since he doesn't have enough tact to be discrete about his hobby..."
That is utter bullshwellyouknowwhat. There is absolutely no reason why anyone should have to keep your shooting hobby a secret. Granted, many choose not to talk it up a lot, but that is their business.
Now, onto the school. I do hope they get their butts sued off. What's next? You take your child to a gunshow, because he/she like you is interested in firearms? The kid has a blast, and doesn't wash off the 'HRL gunshow' stamp on his hand, and shows it to kids at school (as in 'look where my dad took me' not 'I went here and bought a gun so I could kill you!') Is that going to get you suspended too?
School administrators are getting way out of control. They should have absolutely no say on what a kid does outside of school. Hell, the whole 'cannot drink etc' part outside of school is only enforcable through banning the kid from intramural athletics or similar activities. You can get arrested for underage consumption, go to school and show off your ticket, but the school has no power to expell you or suspend you for that action. If they do, they are in for a world of hurt. That being said, the school can choose to send a kid off to an 'altertative school' because they 'think it woudl fit his needs better' even if they are onyl doing it because they think he is a troublemaker.