If you're on a budget but want to see it all (like me), you've got to go ahead and get the CityPASS. An adult pass for Philadelphia is $62 and includes admission to the top attractions (Franklin Institute, Adventure Aquarium, Big Bus Company and Philadelphia Trolley Works, Philadelphia Zoo or National Constitution Center, and Eastern Penitentiary or Please Touch Museum. My advice is to consider how much time you'll have in the city and calculate the cost of what you plan on doing. If you're just going to one or two places, the CityPASS won't be worth it, but most likely you're planning to go to most or all of the places included and in that case you will save big! The child's pass (for ages 2-12) is $39, but keep in mind some attractions, such as Franklin Institute and Big Bus Company, are free for kids under 4 years.
It was quite stroller friendly but you did have to park outside of some exhibits, and they actually have single and double strollers to rent as well. It took us about 3 hours to see the whole zoo, but we didn't really dilly dally, so you might want to budget a bit more time if you are big zoo-goers.
Our first morning, the ladies at the information center recommended Down Home Diner to us because it was the only place with booths (i.e. stroller friendly; most other merchants had counter dining only). It was really cheap and really yummy, so we went back there the next morning as well! I recommend going to the market early if you have kids. We were there before 9AM and it was fairly empty, no problem with a stroller and toddler running around! We went back to grab lunch to go around noon on our last day and it was a mad house!!
They also had a cute (big) model train display, including Thomas and Percy which especially excited our little boy!