133:1 The following things are prohibited on Yom Kippur: eating, drinking, bathing, anointing, wearing leather shoes, and marital relations. It is likewise prohibited to perform any act of labor or to carry between domains, the same as on Shabbos. Since we must add from the weekday to the holiday, all of these things become prohibited while it is still day, a little before twilight. The same is true as to the end of Yom Kippur: these activities are prohibited until a little after the stars come out.
133:2 Handling food or drink for the needs of children (who may eat) is permitted by some authorities and forbidden by others. If possible, one should try to avoid doing so. (Mishnah Brurah 612:32 says there is no reason to be stringent in this, even in a case where the child is capable of getting his own food.