What's the name of the movie about a kid with a pet skunk?

I'm trying to remember the name of a movie I saw probably 30-40 years ago.  It was perhaps a boy and a girl, siblings.  One of them maybe had a pet skunk that he was hiding, or kept feeding or something.  

At some point, I think they are at a table eating lunch with some adults.  The kid is trying to get ketchup out of a bottle, and is looking into the bottle upside down, and hitting it, and gets ketchup on his face.    (These might be two totally different movies... I thought it was the Mixed up Files of Basil E Frankweiler, but watching it now, I don't think so_