Woburn Safari Park - you can drive around it as many times as you like and there are also several animal enclosures you can walk through such as the tropical birds and wallabies. The foot safari also takes you close to the elephants, penguins, sea lions, monkeys and more. Loads of keeper demonstrations, animal feeding experiences and opportunities to handle animals. There's also a lake with pedal boats and a high ropes course for 5-12s.
There's a Mad Hatter's afternoon tea at the Sanderson. It's pricey, but worth it.