I messed up just last night
. I was trying to make conversation with another "Swim Mom" during practice. She had three blond girls with her, just like herself. Then a man appeared and one yelled "Daddy!" and the others enthusiastically greeted him, also. She and the man chatted for a bit.
I turned to the woman and said "Daddy's little girls". She replied "Oh, the big one is mine, the other two are his, and he's my brother-in-law".
She didn't seem offended, but I made an interesting assumption.