I was raised vegetarian but I didn't have the greatest experience in terms of making sure I had a balanced diet (I had lots of problems like anemia and general low energy, etc.) so I was happy to find this book: Raising Vegetarian Children, by Jo Stepaniak.
I don't have any kids (yet) but I have a baby nephew who my sister wants to raise vegetarian, so I'm definitely going to pass on the book. It's supposed to be one of the most comprehensive sources on how to do stuff like the following:
Respond to criticism from family and friends about their choice or their child's choice
Respect and support their child's decision to go vegetarian even if they themselves will remain meat-eaters
Prevent their child from feeling isolated from family or friends because of his vegetarian lifestyle
Insure that school officials and caregivers understand and respect their child's dietary wishes and needs
Cope with dining out in non-vegetarian restaurants
Celebrate holidays that traditionally involve eating meat