Save The Child At All Cost

As the First Wizarding War reached its peak Voldemort came to the conclusion that he would need an heir. He impregnated a young witch and held her captive until she gave him a child, at which point he killed her. He named the child Xoaie and crowned her Heir to the Darkness.

You can imagine that once the Order of the Phoenix caught wind of this they knew they had to take action. Dumbledore led the team that was deciding what to do about the, at this point, unborn heir. He was losing faith that they would be able to do anything to save the child when James Potter came to him and gave news of his wife's pregnancy.

Dumbledore got an idea. He pitched it to the couple. They were hesitant but in the end accepted the mission. They were to tell everyone that Lily was pregnant with twins and the night that their son was born Dumbledore delivered the Heir to the Darkness to Godric's Hollow.

Dumbledore had kidnapped the child himself, and when he did he obliviated Voldemort of all memories of his child and his plan for her. Dumbledore cast a spell over all of the Death Eaters obliviating them as well. And so, there was no one on Earth besides Dumbledore, the Order, and the Potter's that knew the true identity of the baby.