Biting my nails when I should be writing an article

My mother
has raised three children, and here we all are, healthy and well;
My mother
can change a nappy and scrape half a kilo of pumpkiny poo into the toilet without blinking;
My mother
has been around two days a week, every week, since my children were born;
My mother
gets the squirming, delighted, full-body smile of welcome from the twins that is otherwise only bestowed on Lovergirl and I;
My mother
adores my children with the indulgent, all-accepting love peculiar to grandparents.

Why then, as she disappears up the street with my babies in their pram, on their first ever excursion without me,* do I feel so anxious?

*They're only going for an hour! Or an hour and a half, max. But do you know all the things that can happen in an hour?