Bury Knowle Park
Set in the heart of Headington in Oxford, this park has a great selection for all ages. Featuring possibly the highest swings in Oxford, a sand-pit, zip-wire, slides and a Narnia inspired pirate boat
The park also has large open spaces and some sculptures based on local Oxford authors C.S.Lewis and J.R.R Tolkien (e.g. Smaug the dragon from The Hobbit), and is close to local shops should you need some extra provisions for the day-out.
It has a very small free car-park, but you can park in Waitrose for a small charge (off Old High Street).