I was born in 1942.
The custom back in the forties and fifties was (for most families I knew personally, as well as my own) that NO ONE, adult or child, was routinely served dessert. Fruit was dessert, sugared or not. Sugar and other ingredients were in short supply and relatively expensive during the depression and I think this was kind of a carry-over attitude.
Desserts were served for special events only: Thanksgiving, Christmas, Easter, birthdays, etc. But I never recall an instance where dessert, when it WAS served, was not made available for all dining participants, not just adults. [Obviously if you were too young to eat "table food", then you were also too young for dessert.]