Chinuch Hora'ah of the Day:
We see tangibly how it is often possible to exert a greater influence on one’s children through friends than is possible through direct influence, even from the closest family members. The friend should speak to the child about the matter once, twice, or multiple times, and with words that emanate from the heart. It should not be recognizable that the friend is acting as the parent’s agent.
(Igros Kodesh, vol. 24, p. 201)