I can't say enough about Wallingford Playfield! I was introduced to the park during a visit with my 2 year old, and he could have stayed there the entire day or even weekend, if I'd let him.
It has a number of different play structures as many parks do, but these seemed very well maintained (almost brand new) and had a good variety of things to occupy the kids. Aside from the play structures featuring several different slides, it had swings, a carousel, sand pit and digger, etc. What set this place apart though was a good sized wading pool for the toddler set, complete with stones for jumping across and a hidden little hiking trail for the more adventurous. Picnic tables, nice rest room facilities, multiple fields, etc. - pretty much anything you could ask for in a neighborhood park was here. This will be the first place our son will want to go to on our next trip up here.