The girls and I were at the local Jewel store doing some grocery shopping. Since we shop there often, we recognized all the clerks. One woman smiled at the girls and said, "Are you twins?" The girls said, "No, we're sisters." I looked at them and said, "Actually, you are twins." Turns out we never told the girls they are twins.
Maybe it's because we have two girls, but we NEVER call them "the twins." Once you dub two children "the twins," they morph into one person. People see them as a unit. We always say that we have two daughters who happen to be born on the same day. The girls giggle every time they say "we're twins!"