Here are some suggestions to help you do this:

Teach your children to eat when they are hungry
Create a structure around food. Feed your children three meals a day
with a couple of snacks. Try to keep meals at about the same time
everyday and don't fight about how much your child has had to eat.
Allow your child to have snacks in between well-balanced meals, but
not so much that they aren't hungry at meal time. In addition, let
them have desserts and other things they love. Children are much more
in touch with their body's signals than many adults. Trust them to know
what they need, to balance it with what they want, and to stop eating
when they are full.

Avoid using food as reward, punishment, or to cover up feelings
Teach children that food is about fueling the body, rather than a way
to feed emotions or as a reward for "being good." Most of clients have
these beliefs. When I talk to groups about food issues, I often
playfully mimic a mother saying, "here, have a cookie, you'll feel
better" to demonstrate this.

Don't Diet
One of the leading causes of eating disorders is dieting. The ANAD
(National Association of Anorexia Nervosa and Associated Eating
Disorders) Newsletter, Summer 2001pointed out that "three of the most
powerful risk factors for the development of an eating disorder are
(1) a mother who diets, (2) a sister who diets, and (3) friends who
diet. In addition, girls and women who diet severely [restricting food
to excess] are eighteen times more likely to develop an eating
disorder than non-dieters."

Discourage children from talking about other people's weight
Teach your children to see beyond how a person looks. Teach them to
focus on a person's talents, abilities, hopes, values and goals. The
days of judging someone based on the color of their skin or by their
religion is over (or, at least we think it is). Yet, fat
discrimination persists.

Don't comment on your own weight in a negative way
Nothing teaches "hate your body" more than hearing your mother or
father do it. Your children's image of themselves is greatly
influenced by you, the parent.. If you think you are fat (even if you
are not), and see it as a bad thing, your child may eventually see
themselves this way too.

Never comment negatively about your child's (or anyone else's) weight
Some parents think they are being helpful by telling their child to
lose weight or no one will like them. I understand the desire to do
this... after all, in our society this seems to be true. However,
doing so can not only lead your child to feel deep shame about
themselves but can continue to send the message that there is
something wrong with fat people.