I looked around. The girl had looked like she was of sub-Saharan descent, though relatively light-skinned - maybe of mixed race? But none of the families in the shop fitted that description. I asked out loud, to the the people there assembled. "Did that little girl who just walked out of the shop belong to anyone?"
No one took any notice - except one boy, aged about 9, with a Sikh top-knot. He was surrounded by several apparent younger siblings, and his apparent mother was bent over a buggy, simultaneously trying to deal with a baby and pay at the till. He came with me to the front of the shop ("Will it look like I'm trying to abduct him?" I wondered briefly). "Where's X?" he threw back at his mother. I didn't catch the name, but it must have belonged to the little girl, because his mother immediately rushed to the front of the shop in an understandably panicked way. There was no sign of the child.
"She seemed to turn right," I said as mother and son ran to the left. I went the other way, to the toyshop next-door but one - and there, sure enough,was the girl, watching some kind of mechanised toy in unworried fascination. I signalled through the crowd to the mother, and she came back and retrieved her daughter, who grinned at me conspiratorially from her mother's arms. ("Perhaps the father is African? Or Tamil?" flashed through my mind, though by now that wasn't the point.) The mother thanked me profusely, and I felt that, whatever the worth of the Christmas presents, I had justified my existence on earth for one day at least.
Now, part of me wants to find a lost child tomorrow as well.