Do you think Mr. Feeny had kids? He seemed to know how to understand Cory and his friends on the show?

No. It was established at the show's start that Mr. Feeny was a widower and he his late 1st wife Lilian had had no children. Thankfully, WHY the couple had been childless was never speculated about on the show but it seems Mr. Feeny became a teacher in part to try to fulfill having wanted to parent offspring. He did remarry the divorced Lila Bolander (played by William Daniel's wife since 1951- Bonnie Bartlett) at the end of Season Six but she also had had no children by her ex.

Yeah I rather had seen Mr. Feeny get married.

Yeah I rather had seen Mr. Feeny get married.

He DID get married at the end of Season Six.

Actually, Lila had never mentioned anything about children or not. So, we can easily assume whichever.