Re: Boxer seems afraid/cautious around kids
He's just a puppy, so the more socialization you can get him, the better! However, a baseball game, surrounded by a bunch of kids trying to pet him sounds like it could be a pretty stressful situation for your dog. I'm not surprised that he wasn't 100% comfortable.
If you can, I'd try to find a less intense (less things going on) situation in which he can socialize with one kid at a time. I know you said you don't know many kids, but take the opportunities you find to build some positive experiences between him and a kid.
In situations where you know it's going to be a bit overwhelming for him, either don't bring him or make sure that you protect him (i.e. don't allow more than one kid to pet at a time, don't allow them to sneak up on him, etc.). You certainly don't want him making negative associations (anxiety, fear, etc.) with kids. All his interactions should be positive.
Finally, if you're feeling uncomfortable about how he's going to react to a child, don't push him. You certainly don't want to risk his life by putting him in a position where he feels he has to defend himself. Learn some basic doggy body language so that you can be more sensitive to the signs that he's anxious. That will help you tons.
It could be, though, it's just a function of him not knowing how to react to so much going on - not specific to the kids.
Julie and the little darlings...
Tess (fawn girl, born 23-Jun-03)
Conner (fawn boy, rescued 11-Jun-05 @ 8 months)