Other mistake: In analogy to David's mishap with the champagne glasses old Mr. Larrabee crushes an olive jar when he sits down. However, in contrast to David he puts the jar into the front pocket of his pants, and olive jars don't break even if you sit on them (remember what he did to one when he tried to get the last olive out.).
Factual error: When David talks to Linus about the consequences of calling off his engagement with Elizabeth he says that their father would take to the bottle and smoke six coronas. Throughout the movie the old Larrabee smokes one churchill after another, but not a single corona, which is significantly shorter than a churchill.