H and I were talking about how cute Asian babies are, and I realized that I actually know why this is.
Asians are slower to mature than whites or blacks (they also live longer). For instance, Asian babies take the longest to develop motor skills and start walking, and Asians go through puberty later. Since this relative youthfulness of Asians applies even to babies, Asian babies are actually more baby-ish (less developed) than other babies. And thus cuter.
(For the interested: this is all related to the relative r-selectedness of Asians, on which see Rushton’s Race, Evolution, and Human Behaviour. Also, Skarphedin has rounded up some recent evidence on race and maturation.)