If you are familiar with Miss Mason, you might immediately question the legitimacy of beginning so early on with reading instruction. CM lessons cannot begin until the child reaches age six, right? That's right. Well, sort of ;) I'll quote the following passage from Home Education:
Time of Teaching to Read, an Open Question.––Reading presents itself first amongst the lessons to be used as instruments of education, although it is open to discussion whether the child should acquire the art unconsciously, from his infancy upwards, or whether the effort should be deferred until he is, say, six or seven, and then made with vigour.
I at least see a window here. On the same page, Mason holds up Susanna Wesley as a pattern we might consider following, and she began reading instruction on each child's fifth birthday. Just something to consider :)