"Both parents change diapers!"

The primary parent changes more diapers, changes "problem" diapers, counts diapers, notices when supplies are low, purchases diapers or selects and arranges for diaper services, determines when a child's diaper size has changed, knows where the new bag of them is, recognizes when a child's needs change or a child is "toilet-ready," makes a point of being educated in the subject, was the parent who considered the pros and cons of what kind of diaper and style diaper bag to use, purchases the diaper bag supplies, knows or finds out what caused and will cure the child's latest incident of diaper rash, makes sure adequate supplies are on hand for trips, doesn't have to ask what to do if there are no more baby wipes, can tell you why it's corn starch not talcum powder, makes inquiry of the child's pediatrician regarding changes in the child's elimination habits or the appearance of stool, keeps track and makes mental note of the young infant's "schedule" for purposes of health monitoring, adjusts the child's diet or medicines accordingly, buys the toilet-training book or video and little seat, thinks these are issues worth discussing with third party caregivers and raises them, cleans up the linens and clothing after those accidents, can tell you the various ages the child reached this or that stage in development, is the parent who more often initiates discussions on this subject with the other parent, didn't hand the baby to someone else when he needed changing during the neighborhood barbeque, is the parent the child calls for when he needs toilet assistance now, and isn't making snide comments about now having reached this point of this web page.  

"Both parents prepare meals for the child!"

The primary parent prepares more meals, shops for the bulk of the food, selects and keeps track of the household food supplies and cooking supplies and food servingware and kitchen cleaning supplies, thinks about the subject, decides what brands to purchase, considers the child's nutritional needs, monitors what the child has eaten, discusses the child's eating habits with the pediatrician, initiates more discussions about the child's diet with the other parent, reads those recipes in parenting magazines, thinks in advance about what will be prepared for the child to eat, becomes educated on vitamin supplement needs and purchases them when necessary, decides when the infant is ready for introduction to table foods and what foods, asks the child's babysitter what the child ate that day, considers and advises the child's other caregivers on what the child may eat or prefer, as well as the location of food and supplies, does the remembering of what fill-ins need to be purchased and picks these up on the way home from elsewhere without being prompted, can tell you what the child ate yesterday, bought the child's bottles and first sippy cup and utensils, decides whether the older child will purchase lunch at school or bring lunch, suggests and serves snacks, packs food and snacks for family trips, determines the frequency and timing of children's eating schedules, cleans up after meal preparation and sees to (does it or oversees) the overall cleanliness of the kitchen, including oven, refrigerator and other food preparation appliances, keeps track of food prices and budget, and is the parent, who upon reaching this point in this web page is likely to be thinking something along the lines of "wow I really do all this without even realizing I'm thinking about it," whereas the other parent... well, didn't think about it.

"Children impact BOTH parents' lifestyles!"

Which parent always announces (again) a departure from the home while on the way out the door, following a prior announcement and schedule check with the other parent or caregiver, and an inquiry to make sure that the other is fully aware that that parent will be temporarily unable to supervise the child, and that the other has affirmatively recognized the need to switch priority attention and become aware of the child's whereabouts and needs?

Even in households in which fathers stay home and put in more work-time hours caring for the children, and thus are characterized (usually incorrectly) as the "primary caregiver," studies show that these men do NOT perform all of the functions required to provide a home environment and complete nurturant care for their children.

See, e.g. http://www.slowlane.com/research/FAMJOU.html

[A] comparison of the nurturing roles in primary caregiving father and primary caregiving female families revealed marked differences between mothers and fathers. In the primary caregiving female family, the child most often turned to the mother for nurturing. In the primary caregiving father family, the child utilized both parents for nurturing, but still turned more often (56% of the time) to the ostensibly "non-primary caregiving" mother. The study's author fudged this a little: "While primary caregiving fathers may be 'capable' of nurturing, the child preferred the working mother as often as the primary caregiving father when both were available. As a consequence, the working mothers were providing an equal share of the nurturing in primary caregiving father families. "

Frank, Robert A. (1996) "Is the male in child care role changing? Primary caregiving males demonstrate the changing family structure: Implication for social work practice."; Frank, R. A. (1993). The role of the primary caregiving father. Unpublished doctoral dissertation. Loyola University, Chicago.; Frank, R. A. (1995). Who?s watching the children? Unpublished report. http://www.slowlane.com/research/index.htm

"[W]hen the working mom comes home, she tends to move back into her traditional role. For example, she might help with dinner, and she does the bath and the bedtime routine."

"Working mothers tend to know what their child's schedule is (i.e., classes they take) even though they are at work all day. Traditional fathers generally don?t know what their child's schedule is."

"63% of the at-home fathers felt somewhat isolated, compared to 37% of the at-home mothers."

http://www.slowlane.com/research/laymen_research.html