ב"ה, י"א תמוז, תשי"ד
ברוקלין.
שלום וברכה!
... מ"ש אודות כיסוי הראש בילדים, הנה בטח ראה קטע מכתב כ"ק מו"ח אדמו"ר שבענין התספורת, ומשמע שמזמן התספורת היינו מן שלש שנים בודאי והרבה מקדימים גם לפני זה...
B"H, 11 Tammuz, 5714.
Brooklyn.
Shalom u'Vrachah!
Regarding what you wrote about head covering for children: surely you have seen the excerpt from the letter of my father-in-law, the Rebbe, that in connection with the first haircut (upsherin), it is understood that from the time of the haircut—that is, from three years old for sure—and many begin even before this...
Summary
The Rebbe teaches that boys should have their heads covered starting at age three with their first haircut, and many families begin this practice even earlier. This emphasizes the importance of instilling modesty and Jewish identity from a young age.