I think that weight can creep up on you though. I was always a size 12-14 until I had DS2 (10 years ago this year), never really lost baby weight and was in an abusive relationship where fat was my protection, the fatter I was the less my Ex bothered with me :(
I am a size 22 now, I hadn't weighed myself for 10 years (I was a size 14 and just under 11 stone then) and was horrified to find I am now 18 stone. I knew I had put weight on, but I had told myself it was no more than 4 stone, 5 at worst. Most overweight people I know have no idea what they weigh, and wear loose/stretchy clothing so don't necessarily 'see' the weight gain.
I am 7 stone overweight, which is a huge and disgusting amount. I know - and am sticking to low fat foods to try and shift it (lost half a stone in first week) however I am under no illusion it will not be easy. I work full time, in a sedentary job where I sit at a desk for 8/9 hours a day, and spend over 2 hours a day commuting. When I get home I am shattered, I can do some housework/cook dinner but going to the gym in an evening, or for a run? I can't see how I could even though I know this would speed up weight loss.
Children are the same. When I was at school 25 years ago, we had school teams for every sport, did PE or games at least twice a week, and out of school spent our time playing out in the streets and fields near where we lived. My DSs have 1 games lesson per week, and this rarely involves any aerobic activity (DS1 in year 8 spends games lessons playing table tennis...well 15 mins playing, the other 45 waiting for a 'turn' on the table). Their schools have no sports teams. DS1 is keen to play rugby, but his teacher hasn't got round to it yet
. Neither of the boys have friends in the immediate area, so no-one to 'play out' with. I suspect they are not alone, and this lack of activity at school and home for many children is storing up huge problems for the future.