Children carry with them the continuation of the species and all things associated with society. Therefore, the greatest responsibility any parent has is the proper raising of his or her children. With this in mind, from a religious standpoint, there are two "primary responsibilities" of parenthood when it comes to children - 1) providing for the body; and 2) providing for the spirit.
Biologically, however, it is only the care of the body that is acknowledged. From that perspective, since physical nurturing is a very natural extension of pregnancy and early infancy, women historically and biologically are given that as their "primary role" for their children, with men assuming the overall responsibility for physical "support" that allows the pregnant and new mother to focus on the child who cannot live without his mother's nourishment. In this context, man's role has been to make woman's role possible.
Remember, throughout history, providing for the physical well-being of family alone often required full-time focus - from at least the mother and often the father, as well. However, the female role generally was tied absolutely to the child, while the male role was less tied to the physical location of the child. It is a conceit of riches that allows such responsibility now to be split or accomplished part-time.
In modern terms, man's primary responsibility has been to provide, and woman's primary role has been to nurture. When "spiritual care" is introduced into the picture, there is no such biological delineation. There is no "natural" nurturer or provider in spiritual terms. Therefore, it is critical to make allowances to the historic, biological separation of primary roles when raising children within a religious setting.
Interestingly, spiritual care is not mentioned explicitly in terms of spousal roles in "The Family: A Proclamation to the World". What it addressed is the physical care of children only. Further, due to the wide range of familial situations in our modern world, it softens the historical roles by adding two critical addenda:
1) "In these roles, husband and wife are to act as equal partners.”
2) “Individual adaptation” is fine whenever possible and appropriate.
This individual adaptation from the general, historical model to an appropriate personal arrangement is the ideal - structured to provide proper care of combined partnership, but flexible enough to allow for personal choice in unique implementation.
It always amazes me when people criticize "The Family: A Proclamation to the World" in regard to this particular issue, since it is an amazingly concise statement of both the historical reality and the modern ideal.