Q. My son is of the age of chinuch, can he count sefirah with a brocho before the zeman, since his bed time is before the zeman?
A. Shaarei Teshuva (489: 20) writes that a minor who has reached the age when he can understand what sefira is, should count and recite a brocho.
Mibeis Levy (p. 84) and others mention that he should not count with a brocho before the zeman.
Yad Besfiras Haomer (23: p. 51: n. 2) quoting Horav N. Karelitz Shlit’a mentions that if the minor goes to sleep before the zeman, he should rather count during the day without a brocho.
Horav Shlomo Miller’s Shlit’a opinion is that it means he should count the next day in the morning without a brocho.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a