One of the disadvantages of day care is that we don't have a whole lot of control over what words the girls are learning during the day. We're often surprised in the evening when they say something that we've never used at home.
"Butt" is the one of the first items we noticed. Eric and I have always used the term "bottom" around them and encouraged its use. However, when naked, they love to turn around and point at their bottoms and say, "This is my butt." They know it annoys Daddy and continue to do it just to get him riled up. It always ends with Madeleine just saying "butt" over and over again.
Regarding bodily functions, we've always called passing gas "toots." Lily will often remark that she has toots or has to make a toot. Last week, I could tell Madeleine passed some silently, and I asked if she needed to go poop. She smiled at me and said "I farted!" before running off to the bathroom.