Hi, Welcome to Montclair. You're lucky to live in a beautiful and active community. I know there are a lot of MPOA sponsored events throughout the year. If you're looking for something with children his age and for a chance to bond with other mothers, have you considered joining a Mother's group? When I moved to Woodbridge last year I joined the Prince William County Stay at Home Moms Meetup http://sahm.meetup.com/1408/
I enjoy the meetups and playdates and have made some lasting friendship as have my children. I joined when my youngest was just a few months old.
There are other mother's groups out there, the MOMS club of woodbridge, for example. I am not a member but I was a member of the MOMS Club of Springfield and it was a similar experience.
Another group that is beneficial for Moms in particular is MOPS. http://www.saintmargaretschurch.org/content.cfm?id=2088
I'm a member of this chapter.
I recommend going to a few events from a couple of groups to get a feel for the members and the type of events and the overall group before you join or two or all three! =)
Feel free to contact me directly if you have questions.