So-called "motherly heart" is the spirit of fathers and mothers. ... Without regard for their own poverty or wealth, "parents" earnestly turn their thoughts toward raising their child. Without regard for whether they themselves are cold or hot, they shade the child or cover the child.
A "motherly heart” is a heart which maintains the Three Jewels as a parent cares for a child. A parent raises a child with deep love, regardless of povertyy or difficulties. Their hearts cannot be understood by another; only a parent can understand it. A parent protects their child from heat or cold before worrying about whether they themselves are hot or cold. This kind of care can only be understood by those who have given rise to it and realized only by those who practice it.
-Dogen, Tenzo kyokun
You are not a mother/father just by giving birth to a child, it goes deeper than that. It is not until you give yourself up in favour of the child that you become a mother/father.
When you think of your childs wellbeing before yours, when shading him in the sun, giving him your coat when cold, thats when you go from being parent to being a mother/father.