We have to bite the bullet.
I have struggled with my weight pretty much ever since he was born. I have done SW before and had some success but, as always, lost my way and piled it all back on.
Ds was never big as a child but over the last couple of years he has started to get bigger. At first I put it down to his age, changes in his body etc but we can't ignore it now.
He is starting to get down about it but has zero willpower - wonder where he gets that from!
He plays rugby so is big built and he actually hides his size fairly well. However we weighed ourselves yesterday and I was horrified at what he was. 
I had said I was going to go back to SW and he has asked to come. I wasn't sure at first but having read their literature on 11-15 year olds it all sound sensible so we are going to give it a go, starting next Tuesday.
Hopefully we can be each other's motivation and keep each other on the straight and narrow.
Wish us luck, I think it will be a steep learning curve for ds.