child, wife and children, servant, slave
孥 centers on a dependent person in a household: a child, a wife and children collectively, or a servant or slave bound to the family.
孥 combines 奴 (servant, slave) with 子 (child), suggesting a child of a servant or a dependent person. The exact historical development is uncertain.
A servant (奴) with a child (子) below: picture a household where the servant's child is also bound to the family, representing a dependent child, wife and children, or a slave.
For ド, imagine a servant's child playing with a toy door (ドア): door -> ド, and the child is a dependent in the household.