While looking for answers to another question about orcs on Quora, I read an answer that referred to Gollum killing and eating an orc child in the Hobbit, but I don't recall coming across that when I read the book (though to be honest I haven't ruled out repressing the memory)- did this actually happen in the book, and if so, where?
5I don't think he could stop with just one.– SpencerMay 24 at 17:54
He likes eating the "small ones" because they are softer and easier to kill. What makes an orc child is another question. It's kind of opaque.– frеdsbendMay 24 at 18:44
Gollum's last meal prior to when we meet him in The Hobbit is said to have been "a small goblin imp", and later described again as "young".
And still sometimes he put [the Ring] on, when he could not bear to be parted from it any longer, or when he was very, very, hungry, and tired of fish. Then he would creep along dark passages looking for stray goblins. He might even venture into places where the torches were lit and made his eyes blink and smart; for he would be safe. Oh yes, quite safe. No one would see him, no one would notice him, till he had his fingers on their throat. Only a few hours ago he had worn it, and caught a small goblin-imp. How it squeaked! He still had a bone or two left to gnaw, but he wanted something softer.
“My birthday-present! Curse it! How did we lose it, my precious? Yes, that’s it. When we came this way last, when we twisted that nassty young squeaker. That’s it. Curse it! It slipped from us, after all these ages and ages! It’s gone, gollum.”
The Hobbit - Chapter 5 - "Riddles in the Dark"
John Rateliff, in The History of the Hobbit, says that this is our only encounter with an Orc child in all of Tolkien's writings.
The ‘small goblin-imp’ captured, throttled, and eaten by Gollum is probably our only encounter in the legendarium with an orc-child. Again, see [the later passage] for Tolkien’s description of it as not just ‘little’ but ‘young’.
The History of the Hobbit - "The 1947 Hobbit" (i) - Text Note 13
In The Lord of the Rings it's perhaps further implied that Gollum specially eats children.
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 rumour 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.
The Lord of the Rings - Book I Chapter 2 - "The Shadow of the Past"
3'imp' means 'child' or 'young' (as well as the demon); although 'impish' sometimes means small I doubt Tolkien would mean a 'small goblin small' by it. May 24 at 15:47
4@PeteKirkham - The dictionary definition here gives the first definition as "a small demon", though the second definition is "a mischievous child". The wikipedia article goes into more detail on the history of the term, it seems possible Tolkien could have just been using it in the supernatural sense, but as a term for a small evil creature as opposed to a demon in the Christian sense. May 24 at 17:48
7As Tolkien, the expert on English linguistics, certainly knew, “imp” meant a twig or new branch, then became a metaphor for a baby or toddler (a new branch of the family tree), and after that had become the primary meaning, shifted again to “a noisy little monster” and finally “a small demon.”– DavislorMay 25 at 0:23
3I'm also thinking of We Didn't Mean to Go to Sea, wherein the boat Goblin had a dingy called Imp, @Davislor. That association, of an imp as a small/young goblin, is certainly not uncommon.– TRiGMay 25 at 2:34
3@NigelFds - Orcs reproduce same as men and elves. Ignore the movies.– ibidMay 25 at 23:40
Yes, Gollum did kill and eat young orcs (goblins) for centuries when he lived beneath the Misty Mountains, but there is no mention of Gollum killing and eating an orc child in The Hobbit. The only reference to Gollum's cannibalism in The Hobbit is that he intended to eat Bilbo after the Riddles in the Dark.
Citations:  https://fictionhorizon.com/is-gollum-a-cannibal-and-does-he-eat-babies/  https://www.reddit.com/r/tolkienfans/comments/1kl17u/gollum_eats_babies/  https://en.wikipedia.org/wiki/Gollum
6While I appreciate that you've attempted to cite some sources here, none of these seem like good sources, as none of them are actually official. Any of the official LotR books, movies, or games would make for much better sources. May 25 at 9:11
9When providing a link to a source, it's also preferable to include a relevant quote or image from the thing you're sourcing within the answer itself. That way, the relevant information will be preserved within the answer even if the link goes down at some point in the future. Plus, it saves people the trouble of potentially having to search through a lengthy web page to find the specific part that's relevant to the answer. May 25 at 9:15