Would you bring your kids to someone else's house, unannounced?
My mom is a member of a bluegrass group, and they have meetings at our house once or twice a month. Today, one of the members of this group (whom I've never seen before, so she's either new or someone's wife/sister/whatever) and she brought her two-year old with her. I don't like kids, and I especially don't like surprise kids. Mom had no idea this child was coming until she heard it talking to itself as it entered the house.
Even worse, the owner of the child didn't bring anything to amuse it. No books, no crayons, no toys. Nothing. So first my mom looked to see if we had anything suitable, but we haven't had a kid that young in this house for twenty years. Naturally, we have nothing. So they give the kid a permanent marker - a sharpie! - and a piece of paper and she starts scribbling on it. You just KNOW that the two-year old is going to eventually miss the paper and permanently ruin our table.
I think it's horribly tacky to bring a child to someone's house without asking - especially when the person is, at best, a very casual acquaintance and at worse a complete stranger. But if you do have to bring a child with you due to some sort of emergency, give it a way to amuse itself! I mean, how hard is it to keep a coloring book or a toy doll or WHATEVER in the car?
I had some painting to do tonight, but I don't really want to play with toxic chemicals while some munchkin is wandering around looking for stuff to stick in its mouth.