In 3 Nephi 19:29, the preposition unto was accidentally omitted in the 1837 edition. Here in 3 Nephi 20:7, the 1874 RLDS edition has the same typo. This kind of error is natural since in modern English we typically omit the preposition (usually to, but also unto in archaic English) in expressions like this one. Even so, the original Book of Mormon text is about equally divided in usage here, with 29 occurrences of “give them” and 31 of “give unto them” (there is only one instance where the preposition is to, in 2 Nephi 9:26). The 1908 RLDS edition restored the use of unto in this passage, most likely by reference to the printer’s manuscript. The LDS text has maintained the original reading with the unto, as will the critical text.
Summary: Maintain the original preposition unto in 3 Nephi 20:7 (“but he truly gave unto them bread to eat”).