Two little girls wade into the Oxford comma debate

In which two of my daughters debate the Oxford comma, sort of:

C. (age 7): "Dad, what's 'Sarah, Plain and Tall' about?"

Me: "It's about a girl named Sarah, who is apparently plain and tall."

C.: "How do you know that?"

Me: "From the title of the book."

C.: "What if it was about three people -- one named Sarah, one named Plain, and one named Tall?"

L. (age 9): "It's not. The title would have to have commas."

C.: "It does have a comma."

L.: "But it would need more for there to be three people."

C.: "No it wouldn't."

L.: "Yes. It would need a comma after 'Sarah,' and another after 'plain.'"

C.: "No it wouldn't. It just needs one comma to make three people."

L.: "[C.]! I'VE BEEN TO SCHOOL! I KNOW WHERE COMMAS GO!"

C.: "No, it--"

L.: "DAD, WILL YOU PLEASE TELL [C.] THAT I KNOW ALL ABOUT COMMAS? SHE THINKS I'M STUPID!"