Hold up, Damien was 5? Five years old?

Just saw the scene where the nanny says to Mrs. Thorn “Do you think a five year old will understand the goings on of an Episcopal wedding?”

I thought Damien was 2 or 3, not 5! The kid doesn’t even talk. Most 5 year olds are in kindergarten, learning to read and count. You’d think this 5 year old would be even more precocious but he is so babyish.