Does gollum eat a baby in the books? I don't think he does in the movies. I don't remember that from the books either, but there is more description of what got him kicked out of the town there. I thought he was just stealing stuff and becoming more and more creepy.
There is evidence in the Hobbit that he eats young orcs. While your orcs do not imply that they are babies, there is another hint in the Books:
'Then why didn't he track Bilbo further?' asked Frodo. 'Why didn't he come to the Shire?'
'Ah,' said Gandalf, 'now we come to it. I think Gollum tried to. He set out and came back westward, as far as the Great River. But then he turned aside. He was not daunted by the distance, I am sure. No, something else drew him away. So my friends think, those that hunted him for me.
'The Wood-elves tracked him first, an easy task for them, for his trail was still fresh then. Through Mirkwood and back again it led them, though they never caught him. The wood was full of the rumor of him, dreadful tales even among beasts and birds. The Woodmen said that there was some new terror abroad, a ghost that drank blood. It climbed trees to find nests; it crept into holes to find the young; it slipped through windows to find cradles.
I guess with a little bit of imagination, it’s not that unlikely that he had eaten the babies of the woodmen of Mirkwood.
On top of this, he had a discussion with Sam about the best way to cook rabbits, and Gollum said:
They are young, they are tender, they are nice. Eat them, eat them!
So he likes his rabbits young! Which seems to be a preference of him.
Are there orc babies? The films had a bit where they popped out of a pod-thing fully formed, but I don't remember if that was based on anything in the books
The origin(s) of orcs were explained two different ways (i.e., inconsistently) by Tolkien: the orcs were either East Elves (Avari) enslaved, tortured, and bred by Morgoth (as Melkor became known), or, "perhaps.. Avari [(a race of elves)].. [turned] evil and savage in the wild", both according to The Silmarillion.
The orcs "multiplied" like Elves and Men, meaning that they reproduced sexually. Tolkien stated in a letter dated 21 October 1963 to a Mrs. Munsby that "there must have been orc-women". In The Fall of Gondolin Morgoth made them of slime by sorcery, "bred from the heats and slimes of the earth". Or, they were "beasts of humanized shape", possibly, Tolkien wrote, Elves mated with beasts, and later Men. Or again, Tolkien noted, they could have been fallen Maiar, perhaps a kind called Boldog, like lesser Balrogs; or corrupted Men.
Huh, interesting. I knew about the Morgoth corrupting them part and also making them of the earth and/or beasts, but somehow I'd forgotten any descriptions where Tolkien writes that they breed like normal Elves and Men.