There is scriptural evidence to indicate that Job commemorated his sons birthdays.
The ancient Israelite's held a feast on the third birthday of a child, to celebrate the child's weaning.
A birthday is a wonderful way to let the child know how much it is loved, and to commemorate the gift of life.
Children are a gift from God, the Society says, and a birthday dinner (without all the pagan stuff associated) would be a wonderful way to make the children feel loved and to say thanks to Jehovah for the gift of children.
The JW stance on birthdays is just another fanatical, contrarian position that is so hurtful to children that was developed by single, childless, life-long chronic masturbators like Fred Franz to create a sense of being somehow different and special, set-apart from "Babylon the Great" and the world.