Thanks for that we are going back to the Yorkshire Arboretum on Sunday the 3rd September as they have a Teddy Bears' Picnic and you can decorate teddy biscuits. However we did go to Eden camp and loved it thanks for the suggestion.
I took my nieces to Eden Camp on the Coastliner. Not so much an "activity" and but definitely outside and there is a good adventure playground there. Would recommend the museum content for kids aged 8 and onwards, though our 7 year old enjoyed it, even if she couldn't fully understand the historic content of the exhibitions.