M.,
Hey - I am also due for my third, but not until June... Our oldest just turned 4 and my soon to be middle babe just turned 2! We are proud members at the Morris Arboretum in Chestnut Hill - it is amazing there and their programs with nature are incredible! It is so great to take the kids there and just let them run around. Plus, they have the garden railroad that is opening, I think at the end of May. In the summer, they also have the summer concert series in the open meadow and they usually have beer tasting and you can pack dinner as well. It is a great place if you love the outdoors!
We are both teachers (my husband and I) - although I have not returned once I gave birth (I taught kindergarten in Philadelphia) and we don't believe in sending our kids to any day camp since we are home all summer. We have gone camping in New England with both kids (but don't think we'll be doing that with a newborn!) and we frequent the shore. My husband is an avid gardner, so the kids do tons of gardening all summer long.
Best of luck to you and your family!
A.