Don't it make my blue eyes brown...

Charlotte has somehow picked up the phrase, "my eyes are brown," and she uses it to mean "I'm telling the truth" - i.e., "I won't swing Daddy's hammer around! My eyes are brown!" It seems that Pops' efforts to influence the children through telepathy are being thwarted... (For those who don't know Pops: he's fond of saying, "Your eyes are turning brown" when he thinks that someone is full of something other than Truth).