That will always strike me as the weirdest decision to come out of Super's many weird decisions for me.
Chichi was able to teach him what marriage and procreation was and get two kids out of him but she never taught him what a kiss is?
But then again, the previous manga by Toriyama (RIP) Dr. Slump had the wife of its main character Dr. Senbei give birth to a son, something that scared Senbei since he wasn't ignorant like Goku and he knew for a fact that he and his wife never got it on.