Rod Stewart has seven children and one wife who is 26 years his junior -- so it's understandable for a photographer to get 'em confused, right? Not for Rod!

TMZ caught Rod going to Mr. Chow with his litter of kids and their stepblonde last night, and he got a lil' bit pissy when a pap called one of the kids "Penny" -- the name of his current, 36-year-old wife!

Check out the video for his reaction.