When Drosselmeyer brings dolls to dance at the Christmas party, one of them looks strangely familiar; it is really Clara wearing a mask. Children may be disturbed at the moment in which Clara's mask is pulled off and she runs crying to her mother.
Act the beginning of Act II, some frightening-looking creatures menace Clara. They turn out to be her relatives in disguise and she embraces them in relief. No reason is given for this, but this moment is truly strange and parents may have to explain it to their children.
Clara dreams her adventures while the Christmas party is still going on, not afterwards. When she awakens, she is somewhat shaken.