"How young are the little Harvilles supposed to be, though, if they can be tyrannized by boys who are only two and three years old? "

Are you kidding? Toddlers tyrannize everybody, no matter what their age. Think of sensible and capable Anne being tyranized by Little Walter's stout little arms. They are impossible to reason with, they get into everything and they are only just beginning to be able to differentiate right from wrong. The word "no" is completely useless with most children until they are past three and the little Musgroves are extreme examples of toddlers run amuck. You can only keep them in line with too much cake than is good for them (or as Anne and Capt. Wentworth have shown) by vigilent and quite firm in discipline. For older children, having a two year old come and yank your hair and steal your pencil and then not be able to fight back, because after all they are only little and you are a guest...Well that's tyranny!