Chamaco is a colloquial term in Mexican Spanish for a young boy or kid. While it translates to a common word, its regional and informal nature makes it interesting and less common in general Spanish songs.
In the song, the lyrics state, "Pues estaba muy chamaco" (Well, he was very young/a kid), referring to the protagonist's youth when he first observed the harsh realities of the streets. This word adds a touch of authenticity and local flavor to the narrative, making it stand out from more standard terms for 'child'.
"No Es Pa Presumir" is Fuerza Regida tracing a straight line from a rough childhood to the life they live now, and refusing to call it bragging. The opening verse sets the scene plainly: "Desde morro en las calles cosas yo miré" (Since I was a kid, I saw things on the streets), watching a neighborhood he didn't yet have the words for — candles at a corner, a slow pull toward the wrong crowd — before music gave him somewhere else to put that energy.
What follows reads like a tally rather than a victory lap: Nike shoes, a loaded truck, a lit Marlboro, a round of Don Julio. The hook insists this isn't a flex — "Y no es pa presumirles" (And it's not to show off), "Es que es algo increíble" (it's just that it's something incredible) — treating the distance between where he started and where he is now as simply true, not as something to perform.