Many aspects of the Nutcracker rehearsals and show are not accurate. As many companies do multitudes of shows, there tend to be multiple children casts that all perform with the same company of adults. The movie implies that there is only one child cast. Rehearsals are also not so choppy as to what is being rehearsed. One days worth of rehearsal for the kids would be spent on one scene, like the party scene, meaning only those kids would need to be there. There would also be specific rehearsals for only the Claras. Finally, during the show, the backstage assistants would have made sure Isabelle was changed and ready in her solider costume before being able to watch her sister, if she had been able to at all. Also Jackie Sanchez would know to be in costume by the time the snowflakes are dancing. The snowflakes are the last dance of the first act. Jackie, as the Sugar Plum Princess would have already been in costume as she is on soon into the second act and would want to take the opportunity during intermission to warm up with the Prince.
During the show when Isabelle and Jade watch Jackie Sanchez dance as the Sugar Plum Fairy, the music she is dancing to is "Waltz of the Flowers", not "Dance of the Sugar Plum Fairy".
There is no tape on the floor of the rehearsal space. Since the rehearsal space is different from the performance space, the floor would have tape to mark where furniture is and where the edges of the stage are so that when they begin rehearsal on the performance stage, they do not need to re-block the scene.
The movie takes place in Washington DC, which can get very cold in the winter. In December, it would not be warm enough for the kids to be out in the snow without a heavy winter coat.
The movie takes place in D.C during the fall/winter seasons. It would be too cold for Isabelle and her family to have an outside barbecue. The trees in the background would also not have been in bloom, nor would they be green, as seen during the opening pan over D.C.