It is irrelevant whether small is nominally an adjective. The use of adjectives substantively, that is, as the grammatical equivalent of a noun, is well established for millenia.
"Out with the old, in with the new" is a modern English example. "The good, the bad, and the ugly" is another. It was actually a more common practice in Latin and Old English than in modern English.
Most of the time it is done where the modified noun that would have been there is obvious or generic. In this case, it is completely plausible grammatically that "small ones" be contracted to "smalls" with no change in meaning.
If the OED has an example of small being used to refer to children, there's no grammatical reason why they might be incorrect.
Sorry Bess, I was in your camp but Yasamin may have us.