Wow, it's great to come to my favorite site and read that I'm an abusive and neglectful parent because of my son's weight! My 9 year old is definitely overweight, although not quite obese, and it's something I really worry about.
In our case (and, I suspect the case of many overweight kids case) there are a lot of factors that contribute -- among them.
Genetics? DS is adopted, and there's a lot of missing info.
Early history: DS had a structural feeding problem as an infant and toddler and was fed via g-tube on a continous drip. I think this wreaked havoc on his ability to figure out his own needs and get a sense of when he was full. As a toddler if he was hungry he'd refuse to eat -- he didn't get the connection between eating and hunger and putting food in an uncomfortable stomach made no sense to him. In addition, we developed some less than ideal habits -- e.g. when he was finally allowed to start drinking everything he drank had to be thickened -- the only palatable, natural thickeners I could find were sweet (we used applesauce, sweet potatoes, and vanilla yogurt most of the time) so he got accustomed to drinking only sweet things -- it took years for him to be willing to taste water. Also, when he first got rid of the tube his weight fell dramatically -- the doctors gave me a choice between pushing high calorie foods and going back on the tube -- I chose the former, leading to more bad habits.
Activity level: I'd say we get a mixed rating here. On one hand he plays a couple of sports each season, goes to an all day sports camp all summer, and we do things like skiing, going to playground etc . . . on the weekends. On the other hand we live in a tiny apartment, and often get home from work/afterschool care too late to go outside to play. He doesn't have the option of playing outside alone, or doing much active play inside, so if I'm not available to take him somewhere he's pretty sedentary. We also live in the city, and his school's playground is small. It doesn't allow the same kind of nonstop running games I see kids playing in the suburbs.
Asthma: DS has severe allergic asthma. The medications he takes in the fall and spring completely stops his height growth, while increasing his appetite. In addition, his asthma slows him down a fair amount -- so while he still plays soccer, for example, he'll choose to play defense where there's 1/2 as much running so that he doesn't run out of stamina.
Control of food: I make sure he eats a healthy breakfast, pack a healthy lunch and serve a healthy dinner each day -- but he gets snacks at school and aftercare, and is allowed to trade at lunch, also he spends a lot of time at friends houses and gets more snacks and unhealthy meals there too.
Even though I worry about his weight, the worry doesn't tell me what to do -- I feel like I'm constantly facing choices where I don't know what to choose.
e.g. Today I made him whole wheat pancakes -- do I make them with applesauce (low fat, but higher carb) instead of oil? Do I cook them in lots of butter (some people say that saturated fats leave you feeling full longer and lead to weight loss) or a zero calorie spray (low fat but too many chemicals?) I ended up choosing the applesauce and the tiniest amount of canola oil, partially because I was serving them with a couple of slices of bacon (back to that study on saturated fat).
Also making dinner tonight what do I do about fruit and vegetables? Put them on his plate and make him eat it? (clean plate club is bad right, but eating veggies is good?) put them out and let him help himself, knowing he'll eat less? I ended up serving a big bowl of frozen blueberries as an "appetizer" know I'd get more into him whe he was hungry, and then put out a big plateful of raw veggies and told him I wanted him to eat some, but it was up to him which ones -- he chose a bunch of carrots. The strategy seemed to work in that he didn't ask for seconds on dinner, or a snack later in the evening.
Do I tell him he's prohibited from eating the school snack or trading at lunch? If I do am I making him feel judged due to his weight and creating "forbidden fruit" or am I building healthy habits?
His best friend invites him over several times a week, and the playdate often includes dinner of chicken nuggets and mac and cheese, but also a ride to soccer practice (which I couldn't get him to without it) and time to play actively in their big backyard -- a worthwhile trade off?
None of this is easy, and I watch parents of naturally skinny kids making similar choices and not being judged at all.