According to the National Center for Health Statistics, low normal weight for a boy at his fourth birthday is about 12.7 Kilogram. High normal weight is 24 Kilogram as the boy approaches his fifth birthday. Anything in between that doesn't exhibit a great deviation from the normal percentile curve should be considered normal, depending on how far into his fourth year the boy is.
Consistency is Good
If a boy's weight fluctuates far from his own percentile rate, there may be some cause for concern. For example, if a boy who has consistently been in the 85th percentile weight curve suddenly falls to the 25th percentile, doctors may want to find out why.
Normal weight for 4-year-old boys can vary as much as 11.3 Kilogram. By the time a boy reaches his fourth birthday, his percentile of growth curve should be established. If extreme variations from the curve are present, there may be cause for concern.