Odin and his brothers Vani and Ve are the sons of a frost giant. Loki is not a full blooded giant. Loki's father is a giant and his mother is an ogress, so in actuallity Loki is not that large even though he has the power to change size, shape, and gender. After they became blood brothers Odin considered Loki a god, as did the rest of Asgard. It was not until after this that Loki had his three children.