All of the above suggestions are good ones.
If you aren't averse, bidding for travel . com has decent postings for Philadelphia. This can get you under the $130/night price you are seeking. Another good choice is the Embassy Suites, which is across from Hotel Windsor (called the Parkway/Art Museum area). Obviously ES will have a fridge for you to keep foods. You are also a moderate walk from Whole Foods grocery store to purchase any items.

I strongly recommend you avoid driving/parking in the city. The city has a shuttle bus service designed to shuttle visitors between the historic sites and the museums (which include the Please Touch and Franklin Institute) along the parkway. It's called PHLASH and here is the link: http://www.gophila.com/phlash/

As for places for the little CDtraveler to play, there are a few choices. Rittenhouse Square is very nice, centrally located, and good for people watching. There's a big fountain and lots of people bring their doggies. LOVE park is near City Hall and (s)he can watch the older kids skateboard and things. I can't think of any playgrounds with slides/swings, although there may be some up near the Philadelphia Museum of Art.

another good resource: the city's tourism website which occasionally has package deals include museum tickets, parking, or 2:1 offers: www.gophila.com