I think the artist certainly put his own impression of an elfin birth in. Other newborns were shown as being smaller, but it does vary. Human children born today are obviously much larger than human children born in times when food was scarce and mothers had to remain more active.
Although I love that artists (I forget the name though), the picture always did seem out of place. Everyone is cheering in the background, and Tyleet is stretching her arms out, making it look as if Pool literally jumped out of the womb, clean and with fluffy hair. Nice to see Dewshine as a Midwife though, being an equal part in their threesome.
That reminds me, if I recall correctly, Windkin was also magically born without an umbilical chord. I can't be bothered to get New Blood to check.