When the Losers go to the Well House for the first time, someone asks who wants to keep watch, to which 5 kids raise their hands.
Maybe I missed something (only watched the movie once in the cinema), but why do they then split and only Bill, Eddie and Ritchie go in? I can understand that maybe they didn't want to leave anyone alone, but Beverly didn't even want to stay watch, so why did she stay outside as well?