It can get HOT in Philly in the summer! The perfect way to cool off is to dip your toes (or your whole self) in one of Philly’s splash fountains. These 3 are convenient to Center City & the Museum district (Dilworth Park, by City Hall above). Sister Cities Discovery Garden opens at 10:00.
Roberto Clemente Park (Wallace & 19th) is a bit off the beaten path, but still convenient to the museum area and has both a nice water playground and regular playground: