I think being a good role model with eating and activity is the best thing you can do. You can't change genetics unfortunately (unfortunately we all have genetic things we'd prefer we didn't). It's also important not to teach them to have body image issues, which I think is the trickiest part of all these days. A friend of mine lost a heap of weight, completely changing her lifestyle and diet, even to the point of doing serious athletic events, and never, ever talked about losing weight in front of her daughter.