I would definitely suggest the puppy classes at PetSmart. Not that you'll learn the most valuable training methods there
but puppy classes are primarily for the pup's socialization. It will give him a chance to play with other dogs his age and be handled by lots of different people. This kind of socialization is extremely beneficial to his development.
Dog parks are not just risky because of the possible diseases your pup might come in contact with, but also in that you cannot predict what kinds of dogs might be there, and the chance that your pup could run into the wrong dog. One bad experience can have a permanent psychological effect on a pup, possibly resulting in dog-aggression or fear of other dogs later down the road. So... it's probably best to wait until after puppyhood
A better idea would be to socialize him with your friends' dogs, or set up play-dates with other pups you meet in puppy class.
Supervise interactions between daughter and puppy for a while. The pup will have to learn right and wrong of course -- what's OK to jump on and what's not, what's OK to chew on and what's not -- and you don't want him "practicing" on your 2-year-old
especially not with those sharp puppy teeth. Wouldn't make for a such a great experience for her. Once he's learned that humans play differently he should be fine with your daughter. Boxers tend to be very tolerant of children.
Here is an article on bite inhibition that will be quite helpful.
These two outline the stages of puppy development, and give great tips on how and when to socialize your pup.
You can find more puppy training tips in the Articles section of this site... and of course, from us here in the forums