Food is the main reasons as well as lack of sports activity engagement in early age.
Most Asian food do not include milk and dairy on their diet. Dairy food helps the bone grow faster and bigger in early age. In the West, diary food such as cheese, milk are included in their daily stable.
Physical Education(PE) is one of requirement in US curriculum from elementary to high school.
This explain why Asian live in West are taller than Asian in Asia. Yet many Asian in the West still do not include dairy as part of their daily meal. This also explain why Asian in the West still smaller than their peers