Being the parent of a Junior umpire, and having trained them for years, you're actually asking a really good question.
First, you have to be tough skinned. You're going to hear your son be criticised like never before. Fans not only won't like his calls, they'll question why he's even out there, when a call doesn't go their way. It's going to happen, trust me. Be ready for that. If you can't sit quietly by, you'll need to move somewhere else.
Yeah, I'd take a few pictures. But don't be real obvious about. I've got some great ones of my son when he was 11, that are treasures (he's 23 now).
If you're anywhere in the West, consider sending him to the Little League Baseball Junior Umpire Training Academy next June. $300 for a full week of training, where they live at the facility, can't be beat. Here's a link:
http://www.eteamz.com/llbwest/files/...ireAcademy.pdf