I thought I would post my thoughts so far on a few parks we have visited in and around Cambridge, MA.
@ Charles St & Lopez Ave
Good sized, well shaded grassy area and decent size jungle gym. There is a community garden here that if I trusted the area more, maybe I would have tried to use it. This is on our way to the mall, which means I don't go that far too often. There are a few metal seats and a water fountain as well.
Kennedy School Playground
@ 6th St & Hurley St
There are two playgrounds here; a toddler area and a kid area. The toddler area has some baby swings and a small but sufficient jungle gym. There is a metal-frame car to sit and pretend drive on. This area is fenced with a gate you can close. It is shaded and not too large. The larger kid area has a large jungle gym, swings, and a small water spout. Next door there are also some tennis courts, basketball courts, and a soccer field. As this park is three blocks from us, I usually take Nolan here when I want to let him swing.
@ 6th St & Gore St
This is on our way to Shaw's, which I don't walk to that often. There is a small water spout, swings, and it is semi-shaded. It is next door to an indoor skating rink and a large baseball diamond. This playground is mostly fenced. There is an area for bigger kids and an area for smaller kids.
@ Berkshire St & Marney St
There are a few large baseball diamonds here as well as a kids park and community pool. The fields provide an area in which to run around if desired. The playground is not that big or great, and neither is the water spout. The pool is a 3-9 ft pool with no baby pool, and there is a $0.75 entry fee. Parking is limited.
Veterans Memorial Swimming and Wading Pool
aka Magazine Beach
719 Memorial Dr.
Don't let either name fool you. While it is on the Charles River, there is not a beach. Also, I did not see a wading pool, just one large pool. We did not venture in as I wanted a small pool for Nolan. But if you are at MIT, this is close and free!
Artesani Playground Wading Pool
1255 Soldiers Field Rd.
So technically this is in Brighton, but oh well, it was only across the river down near Harvard. This place came recommended and I also recommend it. Large, free parking lot. Two playground areas (toddlers and kids) and both are fenced. It is right on the Charles River and a popular activity is to feed the ducks and geese. You can rent kayaks near-by if desired. There is also a decent size wading pool with multiple water spouts and lifeguards on duty. There are changing rooms. There are many pick-nick tables and large grassy areas. There is a combination of shaded areas and open areas. And oh yeah, it's free.
We have been to Boston Common, but it's not close and was packed each time we were near.
I hope to head across the river to West End and check out the couple parks near there soon.
Here is a little more information on parks in the area. The park map at the second link is just a pdf, so hard to navigate and read due to it's size.