Ideas for a six year olds birthday party in South London

Hiya

My six year's olds birthday is coming up and I'm looking for birthday party ideas. It's during winter time and 10-20 children are to be expected. Happy to get recommendations for entertainers such as Magicians etc. or locations. It's possible to drive to a location as well as there should be enough parents who can drive. Shouldn't cost more than £500. Thanks in advance.