Maia to the rude lady: You know, that's a really poopy question. We are a family, what do you want mommy to say? How about "These two are mine (gesturing to herself and Sage) that one tags along because I married her dad (gesturing to Madison)."
Rude Lady: Harummphhhhh (and storms off)
I'm with most of the PP - it depends on who I'm talking to. I usually just say four. I also have a stepson from my first marriage, but since he's never lived with us or his dad, I don't usually include him. My older kids count him when they tell people how many siblings they have, though. DD loves to make people feel sorry for her by saying "I have two older brothers and two younger brothers, and just me, the lonely girl in the middle."