Gentile – Must one stop a gentile from causing a child to sin:[1] If a child has not yet reached the age of chinuch—defined as being below the age of understanding, as will be explained in Halacha 5—the father is not obligated to prevent a gentile from feeding the child forbidden food, or prevent the gentile from causing the child to perform any other prohibition. Nevertheless, it remains forbidden to instruct or request the gentile to do so, as will be explained below. [Nevertheless, as explained previously, although there is no formal obligation to do so, one absolutely should prevent a child from eating non‑kosher food whenever possible, whether the child is eating on his own or is being fed by a gentile, and hence one should stop the gentile from doing so.[2] The same principle applies to other prohibitions that affect a child’s spiritual purity or modesty, from which the child should likewise be shielded to the extent possible.]
[1] Admur 343:5 “If a gentile feeds a prohibited item to a child who is not yet capable of understanding, the child’s father is not required to protest.”; M”A 343:3; Rabbeinu Yerucham Nesiv 1 in name of Rameh; See Elya Raba 343:3; Kaf Hachaim 343:15; Piskeiy Teshvuos 343:12
[2] Elya Raba ibid; Kaf Hachaim ibid