Were the real birthdays of the children celebrated in Jonas's community in The Giver?
Children in Jonas’s community do not celebrate birthdays in the same way we do. Every child born in a year is assigned a number. Then, once a year in December there is a ceremony where they enter the next age category. The actual month when they were born does not matter. The first December, they all turn One, and then the next year they are all Two, and so on.
Each December, all the newchildren born in the previous year turned One. … Some were already walking, wobbly on their unsteady legs; others were no more than a few days old, wrapped in blankets, held by their Nurturers. (Ch. 2)
Each class has fifty in it, because the community controls the population and makes sure there are fifty children born each year. Unless one of the babies is released, they all turn One on the same day whether they are walking or just born. Thus older kids have a real advantage at first, but it possibly diminishes as they get older.
Like in our world, each ceremony results in gifts. The gift of the Ceremony of One is a name and a family. Babies are born to birthmothers, cared for by Nurturers until December, and then assigned to a family unit. Each family unit has one boy and one girl, and a mother and father who are matched as well.
Most of the gifts are clothes, but there are some more interesting ones. At Nine children are given a bicycle. At the Ceremony of Twelve, they are given their assignment. This will be their job for life. After Twelve there is no ceremony any more. The children are considered adults-in-training. They are preparing for their careers.
When Jonas becomes Receiver and sees birthday parties in the memories, it seems like a nice thing to him.
He had seen a birthday party, with one child singled out and celebrated on his day, so that now he understood the joy of being an individual, special and unique and proud. (Ch. 16)
It is unusual to Jonas that one child would be singled out for a birthday. No one is ever singled out for anything in his community. This is part of Sameness. The only time they ever call attention to individuals is at the Ceremony of Twelve.