It is a well known fact that children need at least half an hour of outdoor physical daily activity. Living in London where the sun does not necessarily make this an easy task, some of the activities listed below may help in some measure. If any one knows of any other schools or clubs other than those mentioned here, please do feel free to offer any suggestions and/or comments.
Swimming
http://magicswimmingschool.co.uk/
http://www.swimmingnature.com/sn-public/aboutus.html
Tennis
http://www.willtowin.co.uk/regents-park-junior-courses/
http://www.ucsactive.org.uk/tennis
http://www.brondesburycoaching.co.uk/junior-tennis-coaching/
Cricket
http://www.lords.org/lords/mcc-cricket-academy/coaching-courses-for-kids/
Football
http://www.littlekickers.co.uk/
http://www.thehillsoccerschool.co.uk/
Rugby
https://www.littlerugby.co.uk/index.aspx
Horse Riding
http://www.hydeparkstables.com/
http://www.londonridingschool.com/contact-us/
http://www.ridinginlondon.com/
Martial Arts
http://www.ucsactive.org.uk/kids-active
Gymnastics
http://www.acorngymclub.co.uk/
http://www.ucsactive.org.uk/kids-active
http://www.teknegymnastics.com/