I don't know about moms of singletons, but as a mom of twins, I find myself counting...a lot.
I count the number of tablespoons each girls gets of cereal or fruit or veggies at each meal (two). I count how many bites of cereal each girl gets before it's the other one's turn (10 bites). I count how long one gets to stay in the Jumperoo before they switch (15 minutes at playtime, 10 minutes before dinner). I count how long I rub their backs when they wake up in the middle of the night (2.5 minutes or 180 small circles). I count how many diapers stay in their diaper bag (8 after running out one time when they visited Grandpapa and Nana). I even count how many pictures I take of them each day so I make sure I take an even amount of each girl.
It's an obsession I tell you. Even when I'm not thinking about how long something takes or how much it needs to be, I still find myself counting in my head. It's very weird, and I'm curious if I'll ever stop doing it. Hopefully one day!