Nephilim!!!

The NEPHILIM offspring four different races;
THE ANNAKIM (they would weigh chains until earth’s core could not support them.)
THE REPHAIM (Your heart will melt in their presence)
THE ZAMZOUMIM (Achievers, Their necks would obscure the sun.)
THE EMMIM (Terrifying ones)
THE GIBBORIM (The strong ones, the giants, the ancient heroes)
The babies were born with a normal size, and then they would grow wildly till their giant state. (Their femoral bone would measure eighteen meters.)
If the father was an angel, we would have a first generation giant, the biggest in size,
If the father is a giant then the child is smaller. And so on .It would explain the small size, for a giant, of GOLIATH