My son was an obese baby. Always around 50th percentile in height and off the charts in weight. Even I was worried. Now at 6, he is the star on his basketball and soccer teams and seems to have 6-pack abs coming through. Not sure when the transition started or ended. We put him in soccer at 4 and he was maybe a little above average. At 5 in the spring there was maybe 2 on his team that were better. Did summer basketball and he started average and by the end of the season was dominant. Did soccer again in the fall and he was head and shoulders better than everyone else and he was a kindergartener on a k-1 team. He is now finishing another basketball season and had to be moved up to a 2nd and 3rd grade team (he is still in kindergarten). Growth can be illogical and funny. Now he eats what he wants and when he wants and just burns it right off.
It’s interesting to look at elementary school class photos from the 1950’s. Overweight kids were rare.