Remember it is more significant if there is a noticeable change in their weight rates than if they remain proportional weight with heights. Covered in more details in the More Happy Healthy Kids 60 day course.
CDC Growth chart Boys 2-20 years https://www.cdc.gov/growthcharts/data/set1clinical/cj41c021.pdf
CDC Growth chart Girls 2-20 years https://www.cdc.gov/growthcharts/data/set1clinical/cj41c022.pdf