Male cats are known to kill kittens, especially if they haven't fathered those kittens, for much the same reason lions do. If they detect that the kittens aren't theirs, they will kill them to bring the female back on heat. They aren't, however known to have them for lunch, or just because they are hungry. Check out www.messybeast.com/kill_kit.htm for more on the same.
Male cats are notorious for killing kittens... they see them as competition. You must keep those kittens away from the tom cat for their safety. He may not eat the kitten perse, but I'm sure the kitten is dead either way.