I find Junie B. Jones books kinda hard to read to my daughter because of the constant bad English/grammar she uses (I know, she's very young, but you have to stop every other sentence to tell or quiz on what the wrong usage is). When your child is in the learning/sponge stage at this age, anything they hear/read is absorbed.
Like the other night at the dinner table when my wife said that someone had a brain fart. My oldest quickly asked, "Brain fart? What's a brain fart?" We had a good laugh over that one and more laughs trying to explain what it was and what "just an expression" is.