Hi there
My 11 year old son attends the gym at Tooting Leisure centre - but at that age you have to attend with a parent/guardian - so not sure if that helps.
Have you looked into sports at all??  Assuming he is in Y7 and has just started secondary school - there are usually LOTS of sporting activities going on there.  Mine plays for both his school and local teams.

But finally - I know as a parent, it can be a concern when a child  seems to be putting on weight, but assuming we are not talking about a worrying amount, I would uge you to keep an eye on what he is eating, but NOT to stress about it too much.  They are on the cusp of purperty and will shoot up!
My eldest was a fairly substantial 11 year old.... he is now a beanpole of a 16 year old!
Feel free to DM me.

Hi

Can I ask for recommendations for activites for an 11 year old. I’m a full time worker often working long hours. I feel like my child is putting on weight which I’m concerned about. I did see tooting leisure centre have a gym session for 11yr olds

Local recommendations for Tooting would be great

Thanks