Use the noun maternity to describe the relationship of a mother to her children.
The state of maternity includes everything involved in becoming a mother, from being pregnant to giving birth to chasing a little kid around a playground. Adoptive mothers experience maternity too, since they are someone's mom. The word maternity comes from the Latin root mater, which means "mother," and it's related to the adjective maternal. You can mostly use the words maternity and motherhood interchangeably.