May i use my 1 and a half year old to be my “shabbos Goy” to turn off lights etc.?
It is not permitted to instruct a child to perform a melachah that involves a Torah prohibition.
According to the majority of rishonim and poskim, telling the child to perform a melachah is considered a Torah prohibition of shevisas beno (see Mechilta on Yisro, 20:10; Rashi and Ramban; Yerei’im 101; Chinuch 32; Rashba, Shabbos 153; Maggid Mishnah, Shabbos 20:7; and see many acharonim, including Mishnah Berurah, Shaar Hatzion 334:54; but see also Biur Halachah 266:6 concerning a child that does something from his own volition, though the Mishnah Berurah clearly writes that when a parent instructs him there is a Torah prohibition).
However, if the child does something for his parents from his own volition, no prohibition will not apply to a young infant who does not understand that he’s doing it for his parents. Therefore, it is permitted to place a young infant next to the light switch, and wait for him to switch off the light.