The Hobbit was originally meant to be separate from his Legendarium
The Hobbit was written before The Lord of the Rings and as such wasn't originally part of the Legendarium, it was later added into the Legendarium after its success and the beginnings of the writings of its sequel, The Lord of the Rings and The Silmarillion. This change occurs in the second edition of The Hobbit where quite a few things change from the original. After The Hobbit, Tolkien decided 'Orc' was a better English translation for the Sindarin 'Orch' or Westron 'Orka' that his works were supposedly originally written in. Tolkien gives us a little insight into is preference in letter 151:
Your preference of goblins to orcs involves a large question and a matter of taste, and perhaps historical pedantry on my part. Personally I prefer Orcs (since these creatures are not 'goblins', not even the goblins of George MacDonald, which they do to some extent resemble).
The Letters of J. R. R.Tolkien — Letter 151, to Hugh Brogan, 18 September 1954
The letter above comes after the second edition of The Hobbit was published in 1951 when Tolkien changed The Hobbit so that it would fit into the mythology he was building and The Lord of the Rings. While its initial setting as a light, quick-paced children's book may have influenced the initial choice of words, the reason words such as Goblin become Orc and Necromancer become Sauron, is because of its introduction into the greater mythology that Tolkien began building decades before The Hobbit.
The word Orc does appear in The Hobbit, 2 times on its own and 6 times as "Orcrist". It is interesting to not that both times it's used on its own it seems to reference larger goblins. This is reminiscent of the original state of the story before its addition into the Legendarium.
not knowing that even the big ones, the orcs of the mountains...
Before you could get round Mirkwood in the North you would be right among the slopes of the Grey Mountains, and they are simply stiff with goblins, hobgoblins, and orcs of the worst description.
This, Thorin, the runes name Orcrist, the Goblin-cleaver in the ancient tongue of Gondolin
They had called it Orcrist, Goblin-cleaver, but the goblins called it simply Biter.
Orcrist, too, had been saved; for Gandalf had brought it along as well, snatching it from one of the terrified guards.
You nearly chopped off my head with Glamdring, and Thorin was stabbing here there and everywhere with Orcrist.
“We have none,” said Thorin, and it was true enough: their knives had been taken from them by the wood-elves, and the great sword Orcrist too.
Upon his tomb the Elvenking then laid Orcrist, the elvish sword that had been taken from Thorin in captivity.