WIY, if you were really so concerned did you offer to help the mother with all her groceries?
One time I was in the local frum grocery and there was a small baby in a wagon sitting alone. Nobody was with the baby and it was soon after the unfortunate Leiby incident. So I waited with the baby until the mother came back. I told her it was not safe what she did and pointed out that she took her pocketbook with her but did not take her baby. She agreed with me.