1. Beis Din – Rabbinical Leaders of city:[1]

Even if a Beis Din sees a child under the age of Bar or Bas Mitzva^[2] transgressing a prohibition they do not need to reprimand or stop^[3] the child from doing so, if the child is doing so for his own benefit, such as eating Treif foods or desecrating Shabbos for his own needs. They are however required to reprimand the child if the child is transgressing a prohibition for the sake of another Jew or if the transgression will become public knowledge as will be explained later on.

[1] Admur 343:1 “A minor who transgresses the words of the Torah for his own enjoyment—for example, if he eats non‑kosher food or desecrates Shabbat for his own needs—the Beit Din is not commanded to separate him [from the transgression]. However, if he does so on behalf of an adult, one must protest and stop him, by rabbinic law, as explained in סימן של״ד. Furthermore, if it is a matter that becomes public and there is concern that those who hear about it may err and say that such a thing is permitted, one must protest even if the minor is acting on his own initiative. For example, if he blows the shofar on Rosh Hashanah that falls on Shabbat, since the sound is heard publicly and people may come to err and say that one may blow [the shofar] even when it falls on Shabbat.”; Admur 301:21; 334:26; 362:17; Michaber 343:1; 2^nd opinion in Rama 343:1; Tur 343; Rambam Machalos Assuros 17:27; Sefer Hateruma 215; Semag L.S. 65; Hagahos Maimanis Shevisas Assur 2; Teshuvas Maharam Ben Baruch 200; Tosafus Nazir 29; Tosafus Yesheinim Yuma 82; Rebbe Padas Yevamos 114a; M”B 343:8; Encyclopedia Talmudit ibid p. 167 footnotes 76-82

Other Opinions: Some Poskim rule that if one sees a child who has reached the age of education transgressing a prohibition, then anyone who sees this, including and especially a Beis Din, must reprimand and stop the child. [1^st opinion in Rama 343:1; M”A 640:3; Elya Raba 640:4; P”M 640 A”A 4; Tosafus Nazir 28b; Tosafus Yesheinim Yuma 82a in name of Yereim; Terumas Hadeshen 94; Rashi Eruvin 96b; Chayeh Adam 66:3] Some Poskim conclude based on this opinion that by a Biblical transgression one is to be stringent and reprimand a child which has reached the age of education even if the child is not his son. [Chayeh Adam ibid; Mishneh Berura 343:7]

[2] Even if the child is over the age of Chinuch [Admur 343:1-2; 2^nd opinion in Rama ibid]

[3] Here the wording of Admur is “separate” or stop while in the other two cases to be brought next he uses the term reprimand or protests, while in the next halacha regarding a father’s obligation the term “reprimand and stop” is used. vetzaruch Iyun on the difference.