Lots of free baby groups if you have a look at Sheffield Family hub site
I second both the above. There’s also Western Park Museum, Graves Park/Farm, and Heeley Farm. All Free 🥰 we’ve been making our way around lots of different parks, but now the weathers getting colder it’s not ideal! Haha
If you drive - the royal armouries in leeds is free and a great day out. I'm looking for similar things too.