And a newborn is far bigger than any penis on earth. Women can take any thickness of cock with ease provided that there is lube.
The salient point is whether it can stretch comfortably without pain. Obviously there is some threshold that causes discomfort, who's to say the limit for some women can't be a girthy schlong?
Your argument is nonsensical. Suppose the different sizes are represented as follows
A = baby
B = thick penis
C = max limit without pain
It's a given that A > B and A > C.
It does not logically follow that B < C