Here are a few ideas of things to do with your child/ren, Please check them for age appropriateness.
Hunt goose, GPS based Treasure Hunt:
Treasure Trails UK: http://www.treasuretrails.co.uk/
Net Mums: http://www.netmums.com/activities
Time Out London: http://www.timeout.com/london/kids
I have been a member of The National Trust since the children were babies they have amazing spaces to visit and organise many activities during the school holidays. It’s a great way of getting the children out of the house and away from technology; teaching them about English Heritage and History: http://www.nationaltrust.org.uk/days-out