As discussed in a previous edition of Daily Halacha, it is forbidden to eat or drink anything from the time Shabbat begins on Friday afternoon until one recites (or hears) Kiddush. Even water is forbidden. This prohibition begins when a person accepts the onset of Shabbat, or at sundown, whichever comes first.
We noted there the lenient ruling of Hacham Bension Abba Shaul (Israel, 1923-1998) that this prohibition does not pertain to minors – boys or girls below the age of Misva obligation. In his view, parents are permitted to feed their children before Kiddush without restriction. It must be noted, however, that Hacham Ovadia Yosef disagreed with this position. He ruled that once children reach the age of Hinuch (training in Misvot), which is generally assumed to occur at around age six, their parents should train them not to eat or drink from the time Shabbat begins until Kiddush. If a need arises, and a child is hungry and thirsty and finds it very difficult to wait, then the child may be fed, but unless this is necessary, Hacham Ovadia maintains that children should not be given food or drink before Kiddush.
Hacham Ovadia also addresses the case of a person who feels very thirsty during Ben Ha’shemashot – the 13.5-minute period immediately after sunset. He writes that if the person did not expressly accept the onset of Shabbat, then he may drink during this period to quench his thirst. The rationale for this ruling is that two Halachic uncertainties are involved. First, it is uncertain whether the period of Ben Ha’shemashot should be treated as nighttime – in which case Shabbat has begun and thus drinking is forbidden – or as daytime – in which case Shabbat has yet to begin, and drinking is still permissible. Secondly, this period may not even be Ben Ha’shemashot at all, as Rabbenu Tam (Rabbi Yaakob Ben Meir, France, 1100-1171) maintained that Ben Ha’shemashot begins later than this period. Given these two uncertainties ("Sefek Sefeka"), drinking may be allowed during this period when necessary. It must be emphasized, however, that if a person had accepted the onset of Shabbat, then he may not drink even during this time.
Summary: There is a difference of opinion among the Halachic authorities as to whether one may feed children (who have reached the age of training in Misvot) before Kiddush once Shabbat has begun. According to all views, however, this is allowed in situations of need, such as if a child finds it very difficult to wait. Although eating and drinking are forbidden once Shabbat has begun before Kiddush, if one is very thirsty within 13.5 minutes after sundown on Friday afternoon, and he had not accepted the onset of Shabbat, then he may drink.