IT's on a different ilk to Alton Towers, Legoland, etc etc, much less grand (and not to mention less expensive ) and if you buy tokens and don't use them all on the day you can keep them and take them with you next time you go.
Definitely need a buggy, but there's lots of space for them just to run around and play too.
With regards to Woburn that sundew mentions, I personally prefer Whipsnade Zoo think it's better value for money, and if you've got young children who "NEED" to see the animals you're safer at Whipsnade .