Q. Can you tell a koton to put the schach lechatchila if his father is there? Does he have to be present the whole time or is it enough only at the beginning?

A. On the onset, a minor should not place the schach on the suka, (since he is not obligated yet on the Biblical level with the compliance of the mitzvah of suka) however after the fact it is permitted. (Mogen Avrohom and Pri Megodim 14: 3, Bikurei Yaakov 625: 2)

If the father or another adult is standing by it is permitted lekatchila. (Kuntress Shiyorei Hamitzvos 3: mitzva 326, Nitey Gavriel – Suka 25: 1)

Horav Shlomo Miler’s Shlit’a opinion is that he does not have to stand by the complete time. It suffices if he instructs the minor to place the schach for providing shade and the kotton acknowledges.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a,