A child of the devil is a devil. Devils are not converted nor is there any account in the entirety of scripture where we are shown "devil conversion." It is non-existent. Devils and devils children are NOT turned into Gods Children.
Gods children arise from the planting of the Seed of Christ in the ground. That ground still contains tares, which are the children of the devil aka demons.
Matthew 13:38
The field is the world; the good seed are the children of the kingdom; but
the tares are the children of the wicked one;
These tares are NOT converted into wheat, but destroyed in the end.
Matthew 13:40
As therefore
the tares are gathered and burned in the fire; so shall it be in the end of this world.