Raymond's father is George's brother Henry. This is the only time during The Jeffersons' run that Henry Jefferson is even mentioned, and he never actually appears on the show. On All in the Family, where the Jefferson family originated, Henry Jefferson was a prominent character, even appearing on-screen before George Jefferson made his first-ever appearance.
Though brothers George and Henry Jefferson were close enough to still live and work together when they were in their forties, this is the only time Henry was ever referred to during The Jeffersons' 11-year run. Since Henry's personal life was rarely discussed during what totaled less than three hours of screen time on All in the Family, it can be assumed that he had a little son somewhere who simply wasn't mentioned.
The Marshmallow Land game that George bought for Raymond is actually the racing board game "Candy Land." They just modified the title from the cover of the box.