On the weekends, we’ve been enjoying the amazing parks and playgrounds in Berlin.
Some parks, like Jungfernheide, are huge and forest-y, with lakes where people can swim and splash. (Some people wear bathing suits, some don’t. Nudity seems much less taboo in Germany than anywhere else we’ve visited. At the DDR museum, there was a part of the exhibit dedicated to nude beaches in the DDR/GDR, complete with photos and videos. )
Another huge park-like space is the non-operational Templehof airport, where people now bike, grill, and play sports. (The hangers are also a currently being used as temporary refugee shelters.)
Berlin playgrounds are also generally lovely, and sometimes themed: witches, airplanes, etc.
Of course, since this is Germany, some playgrounds are attached to beer gardens. Here, Theo and his friend just needed to slip underneath a fence to go play while we parents talked and sipped nearby. 
Theo’s favorite part of the Berlin playgrounds have almost certainly been the very common zip lines.
Overall, the saturation and quality of parks and playgrounds have been amazing here in Berlin! We’re officially spoiled.