Audio problem: When Georg playfully taps Max's cheek, we hear 3 taps but Georg only taps twice.
Continuity mistake: When the captain sings for the first time and hugs the children, Gretl is under his left arm. In the next shot, he raises his arm and she is nowhere to be seen. Then, when Maria motions for Gretl to give the Baroness the edelweiss, she is back under his arm.
Answer: In the film, the Mother Abess explains to Maria that the Captain Von Trapp's wife died "several years" ago. This is commonly misheard by viewers as "seven years." In reality, the actual mother of the Von Trapp children was Agathe Whitehead, who died of scarlet fever in 1922, just four years before Maria came to the Von Trapp home, initially as a tutor (not a governess) in 1926.
Michael Albert