my 2 year old son is tall for his age but only 50th percentile for weight. does that mean he is underweight?
if your child's bmi percentile is in the healthy zone then congratulations! it sounds like your child is at maybe the ~90th percentile for height and a 50% weight so that might be around the 25th percentile for bmi. if the trend is good then your child's growth is tracking along a healthy path. children who have 2 parents with weight issues are at higher risk of obesity that is 13 times higher than the baseline so you are doing a great job. just like i would counsel parents with a child at the 75 or 80th percentiles not to worry likewise feel good about your child being at the 20-25th percentile.