A.U.
I find the best park for little guys is South Park in Hermosa. It's off of Valley Drive right around 6th street. There is only one tiny play area with swings and a train, however the surrounding area is covered with grass for running around when you are just getting your sea legs...
I find the tot lot in manhattan a little too crazy. Valley park is fun but if there are older children there they are always running over the little guys (the same -actually worse--- at Polliwog park).... Fort Lots of Fun off of Prospect is good because it's never that crowded, however it is meant for children older. My son has fallen several times off the structure because the gaps are so high between levels... we've had alot of bloody faces at fort lots of fun....
South park isn't for everyone if you are looking for lots of structures... it's pretty quiet though and very easy for a little one to just hop around without getting trampled on. Great for tricycles and ride on toys...Just bring some sand toys and you are good to go!