Children below age nine: There are no limitations on these children’s eating on Yom Kippur.[1] There is discussion regarding whether this halacha is in order not to jeopardize their health or simply because the mitzva to fast does not apply to them.[2] If it is due to health concerns, one could say that the child’s eating should be limited to her actual needs. However, the practical halacha is to let such a child eat as much as she wants whenever she wants.[3] Even if the child wants to fast, we do not allow it.[4] This does not mean that the child must be forced to eat at the outset. Rather, on Yom Kippur, parents should not allow their children to refrain from eating to a degree that they would normally consider unhealthy for them.

Children age nine and above. The gemara[5] says that healthy children aged nine (or weak children aged ten) should fast “for hours” for the purpose of chinuch[6]. The gemara explains that a child should eat the morning meal an hour after the time she usually does. The Shulchan Aruch[7] adds that the amount of delay depends upon the strength of the child.
The aforementioned gemara discusses delaying the morning meal. Some Acharonim understand this as an indication that the child had not eaten until this point, including Yom Kippur night. Therefore, a child of this age should fast at night, and, at that time, should be given a drink only if she complains of great thirst.[8] Others understand the gemara as meaning that all meals should be delayed during the course of the day.[9] However, once she has broken her fast, if she is still hungry, she may eat regardless of how it fits into her meal schedule.
In a case where a child is permitted to eat, adults are allowed to feed her. If she wants to eat earlier than she should, there is a halachic debate regarding whether an adult may feed her.[10]