I don't have kids, but I spend my life here

and I think I can kind of see what luv2sew was trying to say. When compared to Sesame Place and some of the other destinations geared to very little people, New York's appeal can be a bit less overt for toddler entertainment. Also, it's not the easiest in terms of stroller sidewalk navigation (in parts of midtown, your kid in his stroller literally acts like a battering ram against crowds) and overall cleanliness (I wouldn't necessarily want the kid to touch things outside). That being said, there is a lot of stuff here that little kids would like.
Little-known fact: if your kid likes trucks, most NYC fire departments are totally wonderful with you walking in (you'll pass a bunch with open garage doors) and letting the little guy or gal take a look. They will usually dote on him or her.
I highly recommend Shake Shack, which is next to Madison Square Park down at the intersection of Madison Ave and East 23rd. They have luscious burgers and hot dogs and snacks, and you can carry it out and have a lovely little picnic at the park. Other families will be down there doing it. Your toddler can run off a little energy while you enjoy the sun
P.S. I went to Mars 2112 and, while it certainly wasn't winning any Zagats awards, I found it entertaining as an experience. And isn't an experience what we're essentially after when we're tourists?