In regards to the custom of not cutting a boy’s hair before the age of three – what’s the reason for that?
In my family we follow that custom, so I wouldn’t want to be different. But I’d like to trim my son’s hair ever so slightly (it wouldn’t show), because he has just a drop of hair, and by cutting it, it would grow more (and thicker). If I do that, would it be considered going against the minhag?
The custom of not cutting a boy’s hair until the age of three is mentioned by the Arizal (Shaar Ha-Kavanos 87a), and is generally seen as being related to the mitzvah of leaving the pe’os ha-rosh, in bringing the child to love the mitzvah (Nechpah Bekesef p. 18).
Some add that the three year delay is related to the mitzvah of orlah, and indicates a certain spiritual readiness (Ayalah Shluchah) — according to one Midrash Avraham was three when he discovered Hashem.
The custom is not mentioned by halachic works, and therefore doesn’t carry full “halachic” weight, so that if there’s a need to trim the boy’s hair, this can be done without concern. The custom will still be fulfilled by his having his first “real” haircut at the age of three.