They don't understand that Mother isn't a machine, in that, she does not run on batteries, or gas. You can't wind her up and make her go, when she's out of fuel, or make her legs work, when they've traveled their last mile for the day. Children don't give up, never wind down. Mothers have their own 'looks'. You can usually tell who is a Mother and who isn't, by the way they look at kids, or they way they react to the tantrums some pitch in a crowded fast food restaurant.
Mothers understand children better than other people.
You can usually find the run-away dog, but, if the unruly child isn't seen to at the moment they interrupt you in whatever you are doing, and corrected, shown that it isn't the accepted behaviour, then you will soon have a problem on your hands. Mothers in their prime sounds like Mothers who have gotten half way through the daily chores, and just sitting down for a cup of coffee before the kids come home, or, perhaps raised their kids to teenagers. Not so, for we, in our prime, are those Mothers who have, long ago, sent our kids off to college, a new job, their own apartment, marriage, and now are enjoying the fruits of our labors. We can set quietly in our nooks, enjoying life, in our quiet time, until we again hear the phone ringing, or a knock on the back door. You can even handle an occasional energetic child jumping astride your waist.