Why do you think overweight children come from families with parents who are also overweight

In a way it is endorsement to the children that their eating habits
and lifestyle habits are acceptable. Just like any of us what better
role models than your parents. If they snack and eat unhealthily
then the children will as well.
However having said this, there are other considerations to take
into account. For example there is some tentative evidence that
people who are obese are genetically pre-disposed to it. So if
this were the case, these families may have an underlying reason
for their weight problems. This does not necessarily mean that
there is nothing that they can do to lose weight. Families who
may have these genes who eat eat wisely and exercise will be
showing their children how to eat, how much fun it is to exercise,
and can maintain normal weights. So while genes don’t excuse
bad lifestyle choices, it may be a reason why they are more likely
to become overweight.