I know that parents must be just in giving gifts to their children. But sometimes you may be out with a parent and they may take you out for lunch or buy you some snack. Is it permissible to accept this since the other children won't receive it, although the parent does generally provide for all of the children?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The basic principle is that it is obligatory to establish justice among children in gift-giving. It is prohibited for a parent to favor some of the children over the others with gifts for no valid reason, like being in need and the like. This is what we believe to be the preponderant opinion in this regard among the statements of the scholars. However, singling out some of the children with insignificant gifts that are customarily forgivable is pardoned, and what you are asking about falls under this category, as stated by the scholars. The Hanbali scholar Al-Buhooti said in Kashshaaf Al-Qinaa’: “It is not obligatory to establish justice among children with regards to insignificant gifts, because this is pardonable and does not affect the children.” [End of quote]

Allah Knows best.