Max and Becky are on the playground discussing Olive and her pictures. First Becky gets up and goes over to Olive, then motions for Max to come join them. When Max gets up a compress (or ice pack) is visible just above the knee of her left leg.
Max and Becky are waiting with Becky's mom for Max's aunt to show up as her pretend nanny. After Becky's mom meets Max's aunt, why doesn't she take Becky's back pack home with her (possibly holding Becky's books and homework) rather than making Becky go on her play date with Max having to lug it around with her?
When Max and Isabella are playing the chess game at the end of the movie, there is no way that Isabella could know how many seconds were left on the chess clock before the flag dropped. Chess clocks do not have second hands on them, just a little thing that turns to let you know which clock is running. It does not indicate seconds, however.