Our first child was born in Brooklyn, second in New Jersey, but my wife and I are originally from the Pittsburgh area. Returned to Pittsburgh while our kids were still in pre-school.
The Carnegie Library system is outstanding. The Squirrel Hill and Oakland branches (most convenient locations to us) have large, comfortable children's sections. With their loan system, can request pretty much any book you can think of and pick up in a few days in the branch closest to you. My kids understand the system and use it to get books by authors they like.
Children's Museum, Phipp's Conservatory, and Carnegie museum are all great for kids. Generally, if you go more than once a yearly membership pays off, and a lot of these are connected (membership in one gives you admission to others).
A few years older now, we got season passes to Kennywood and Sandcastle. Kennywood has fantastic roller coasters, especially the older ones.
Schenley and Frick parks are immense. With the Pittsburgh topography, you can walk through trails and feel totally removed from the city.
In many neighborhoods, you can own suburb sized homes for cheaper than the suburbs, with access to all the city amenities.
My kids walk 3 blocks to school.
I could go on. Pittsburgh is a great place to raise a family.