yes, Wimbledon Park is lovely, Fisil. Ducks, the dreaded Canada geese and swans (with their six signets). Yes, they're on the sailing lake. The paddling pool is also open and there's the refurbished sandpit too....
We go to Morden Hall Park a lot too - the River Wandle runs through it - dd goes in fishing for sticklebacks with her net and bucket. There are ducks too. And the garden centre has lots of lovely fish to look at for free (including Nemo and Dory!)
And Battersea Park has the lovely boating lake and nice playground.
Plus duck pond on Wimbledon Common....and the windmill museum is a quid to gtet it - dd and ds love it in there!
hth a bit, Dinny