I've been to Union Square park and its environs many, many times over the past several years. Union Square Park has become one of my favorite parks in the City. It's not large, spanning from 14th St. to 17th St., but it is lovely, with older trees and many, many park benches. There's also a good playground, with separate sections for babies/toddlers and for school-age kids. The latter has a "spinning wheel" that the kids can sit on and get dizzy (to their infinite delight), and a metal climbing cone (you have to see it to understand what it is) that is good for kids 6 yo and up. There are also slides, and things to balance on. Union Sq. park also is, in my experience, safe even after dark because it's well lit and in a well traveled area. The Union Sq. subway stop is serviced by the N,Q, &R lines; the L line; and the 4,5&6 lines, and there are several other subway stops within walking distance. There is a lot of shopping, restaurants and even a hotel (the W) either contiguous or close by.