I once did an internet café, though it was more of a bar, since we don't really have a café type thing (that I know of).
You could do a toy store a-la Mr. Magorium's Wonder Emporium, where kids can come and play with the toys too. Personally, I think the kids' stuff is so colorful that it's really fun to design playrooms and stuff. Maybe you agree maybe not ¯\_(ツ)_/¯
There are lots of useless science and technology thingamabobs and decorations in Get to Work. There's also some interesting technology type stuff in debug. It might be fun to make a sort of secret government/alien base sort of thing! Of course, it wouldn't be a hangout, but you could still "break in" and it would certainly fill the lot.