Kids should be breastfed for a year (at least--WHO says at least two years) and moms who breastfeed longer shouldn't be harassed, they should be applauded. (How many extended nursers have obese kids? I'm very curious. I bet very, very few.) Bottle feeding, aside from formula being a second-rate product, expands a baby's stomach far too much. They can't say no to a bottle! They get overfilled, their stomach stretches, then it's a lifetime of wanting more, more, more.
Food-wise, I blame soda (high fructose corn syrup is bad, bad stuff), fast food, candy, and condiments (like ranch dressing). If your kid is already obese, read Disease Proof Your Child and Eat To Live. See www.diseaseproof.com.