There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact. Maybe your child didn't walk until he was about 19 months. Maybe he didn't crawl until around the same time. No, perhaps he was just very heavy and needed to develop strength that most kids don't.
Variation is important to consider.
Back to the next question. Just because one has less of something than another doesn't mean it doesn't have much. It could just mean that the other has a whole lot of whatever it is. Back to the next question. That still doesn't make them healthy.