One thing we all need to realize is all this bickering means basically dick, because SCOTUS ruled on a similar case back in the 80s:
https://en.wikipedia.org/wiki/Hazelwood_School_District_v._Kuhlmeier
In a nutshell, student newspapers aren't protected by the first amendment because they are school-sponsored and considered limited public forms of expression. Although year books aren't newspapers, they fall under the same umbrella.
So it doesn't matter what you or I or the dad or the kid thinks, because in the end it's up to the school on what to allow or not allow in the products they print.
Like I said before, I'm all about the freedom of expression. If a kid wants to take GST's suggestion and dress up in a rainbow with his two dads for the year book (hey GST, whatever floats your boat, I don't judge) more power to 'em. But all stuff like this does is make schools pull a Toby and whip out the ban hammer. Instead of letting kids be kids and enjoy some creativity with their yearbooks, the next time around it'll be vanilla bland just to avoid any confusion. If one person can't have any fun, than nobody can have any fun. It's just easier that way. Otherwise you give people choices and, well, you know the rest.