Baseball games are great a opportunity to explain the rules to your child. My 3 year old is too young to understand and she could care less about the rules, but my 7 year old was very interested and attentive while I explained the rules to her and pointed things out during the game. Just remember, that your kids may get a bit bored during a 3+ hour game. Later in the game I took my daughters for a walk around the park. We took a look at the city skyline and checked out the field from different angles.
Later in the game we learned a bit about gravity as a few pigeons sat in the rafters above us. The people two rows down from us got nailed twice! Once on the guy's head. I couldn't help but chuckle a little bit, but if it was me that was hit, I would have been pretty upset. :-)