Why do some children get sick more often than other children?

Variables. Infants tend to be well protected from illness in the first 8-12 wks by immunity passed in pregnancy from the mother. As that fades, babies /kids/adults get exposed to a variety of bacteria, viruses, parasites based on lifestyle, hygiene & chance.Kids that are well rested & fed show their peak resistance to illness.Some are more or less ill based on a combo of genetics & exposures.