I totally judge and blame the parents when I see a fat child. It's a horrible thing to do to a child- it puts so much added stress on their bodies, it effects their health, it effects their self confidence, it effects how other children look at them.
Figure out how to change the lifestyle you lead to make a better change for your child, before it becomes something that effects them for life.
For the record, I consider 'fat' to be a child whose belly is rounded and large enough that it presses against shirts and hangover the waste of their pants. If your child is is fat, you need to figure out why, and do what you can to fix it.
If it's a medical issue, it is still your responsibility to figure out what it is, and what needs to be done to help the child.
Since I am sure people will ask, I have 3 kids. My 17 year old is 5'1" and weighs 105, and wears a size 5 in juniors. My 14yo is 5'4" and weighs 106, and wears an adult x-small in adults, and size 14 in kids pants (and they hang off of him). My 10yo is 4'9" and weighs 75 pounds, and wears a 10 in kids clothing.