It's a tricky thing to track - bedevilled with all sorts of factors that skew results.
There is no ethnic component to growth in infancy and toddlerhood, though, squizita. The major data collection that led to the WHO charts came from different settings, deliberately chosen for their diversity, and they discovered that while ethnicity had an influence on size at birth, it did not have an influence on rate of growth thereafter. This was important to know, because slow-growing babies were being missed by HCPs.....'it's ok for this baby not to gain weight because his parents are vietnamese' or whatever. No, it's not ok - or rather it might be ok, but not because of ethnicity.
There seems to be a bit of heredity in slow growth - siblings and close relatives seem to share the tendency. And of course in a western setting with healthy, normal parenting, slow growth can be monitored, and most of these babies are fine.
But it's not ethnicity, and if we assume it is, we will miss babies who genuinely need some sort of intervention, or further investigation.
Will try and find a link that shows an explanation of the research.