We went to my parents for a few days and ended up at High Lodge. Its a huge country park with adventure play grounds scattered all over. Cost us £6 for all day parking. Bought food in the restaurant which was very basic. Bought 2 sausage rolls and 2 childrens lunch boxes and it cost £9. But if we went again would definatly take a packed lunch as there is loads of places to sit and eat. You can also hire BBQ over there.
Overall was a fantastic and cheap day out (and the kids were exhausted on the way home)