1242 —אפשערעניש, תספורת לגיל שלוש, ומנהגי חסידים

B"H, 20th of Marcheshvan, 5712.

Brooklyn, NY.

Haraha"ch vavac"h iy"a nu"n etc. Shmuel Menachem Mendel

Shalom u'Vrachah!

... In response to your notification that on Friday, 6 Teves, may it come upon us for good, it will be three years since your son was born—may it be G‑d's will that you raise him to Torah, to marriage, and to good deeds with abundance. Here is a passage from a letter of my revered father-in-law, the Rebbe, regarding the upsherenish (three-year-old haircut): "... Regarding cutting the hair—'upsherenish'—it is a significant matter in Jewish custom. Its main point is in educating to leave the peyos (side locks) of the head. From the day of cutting and leaving the peyos of the head, it is customary to begin training the child in wearing tzitzis and reciting morning blessings, Birkat HaMazon (Grace after Meals), and Shema before bed. May Hashem help you raise him to Torah, marriage, and good deeds with abundant livelihood and peace of mind both materially and spiritually."

As for your question whether to do the haircut on his birthday or postpone it until Lag BaOmer—if there is no established custom among Anash (our community) to delay until Lag BaOmer, I do not see reason to postpone the haircut and education (as stated above in my father-in-law's letter) for so long. Especially since there is a festival in between and some say (see Sefer Maharid vol. 1:169b) that this haircut relates to 'the beginning of shearing,' which is one of the gifts for Kohanim. At most, you can also cut his hair on Lag BaOmer—that is, make that day the completion of the haircut.

With blessings for mazal tov and chassidic nachas from your aforementioned son and from all your offspring.

Summary

The Rebbe teaches that upsherenish marks an important educational milestone; unless there is a strong community custom otherwise, one should not delay introducing mitzvah observance at age three. The focus should be on beginning Jewish education with joy and abundance.