Me: Oh, you already grabbed chocolates?This led, of course, to me giving an impromptu lecture on the evolution of "nosotros" in Spanish, which, though unappreciated by Grace, I will nonetheless repeat here.
K: Yeah, I got some for work.
Lila (excitedly): Some chocolates for work and some for us-guys! [əm wawI fə wək æn əm wawI fə əsgaiz]
Grace (archly): Lila, it's "us," not "us-guys." Dad, she said Us-guys.
At about the time Spain was busy conquering the world, it was in more or less the same place we are now with its evolution of second person pronouns. Spanish, like English, started out with singular and plural second-person pronouns:
|Various innovative forms|
|2nd person:||You, Thouh||You, Y'all, You guys, Yous, Yous guys||Vos, Tú, Vuestra merced, Usted||Vos, Vos-todos, vosotros, vuestras mercedes, ustedes|
Eventually, Spain evolved four different 2nd person forms to address formal and informal, singular and plural, and "vosotros" became the standard 2nd person informal plural form. It was only after the evolution of "vosotros" that "nosotros" came into being instead of "nos" as the full (non-clitic) form of the first-person-plural pronoun, presumably as an attempt to regularize the forms by rhyming them (of course "nos" and "vos" had originally rhymed, but by this time "vos" was no longer a plural pronoun).
So, what does all of this have to do with "us-guys"? Of course, "us-guys" was formed by precisely the same pattern that formed "nosotros" in Spanish. Just as "otros" was taken to be a plural marker, "guys" is understood by Lila as the plural-marker in my Northeastern dialect. It strikes me that it is quite possible that Lila learned the grammatical meaning of "guys" (turn a pronoun plural) before she learned its literal meaning.
To understand what happened in the Spanish in terms of modern-day English, you would have to imagine the following events taking place in order for English to arrive where Spanish presently is: