Things to in Freiburg im Breisgau with a 4 year-old

Europa-Park. Forget Disneyland, this is where Europeans go. https://www.europapark.de/en

Seepark Freiburg - large lake, very popular park.

Colombischlössle - Archeological museum with interactive displays for kids ranging from prehistoric to Bronze Age. It's really quite good. https://museen.freiburg.de/museen/arco

Wild animal park - https://www.mundenhof.de/

And, if you are over by the Augustiner Museum, look for the alligator in the river.

Buy a rubber duck or two and enjoy the Brächle running down some cobbled streets.

brilliant idea from Mona, but watch for trams and cyclists...

also Schauinsland mountain. Enthralling view from the cable car and summit area (also for adults) and a good childrens playground at the top.

https://www.schauinslandbahn.de/en/aktivitaeten/kinderspielplaetze

tip for afternoons, for an extra €6 on a basic adult round trip ticket for the cable car you can add coffee and cake in the cafe at the summit.