popa-
Some children are more precocious than others. There are definitely some 4 year olds who “get it” and could appreciate the chinuch aspect. And once you have some kids like that, which parent is going to say his little yankele is any less precocious as little Yankele Cohen across the street….
Besides, your 4 year old is only going to shul to run around, anyway. We wouldn’t want him swinging a lulav at the same time, could be dangerous.