Chavalito is a charming and somewhat informal term for a 'youngster' or 'kid'. It's a diminutive of chaval, which itself means 'young man' or 'lad'.
In the song, El Rabbanito uses it to emphasize that despite the tough path he's walked, he remains the same person he was when he was younger: "Yo sigo siendo el mismo chavalito" (I'm still the same kid). It conveys a sense of humility and staying true to his roots, making it a relatable and endearing word.
El Rabbanito's "Cambio Mi Suerte" is a really honest look at what happens when you start to succeed. He talks about how "Cuando tú vas pa' arriba sobran envidias" [When you go up, there's a surplus of envy] and how people who weren't around before suddenly appear, claiming they were there "día con día" [day by day]. He remembers a time when people just laughed at him because his life "no era la misma" [wasn't the same], while he was praying to God.
He believes his luck changed because he's "gente con la gente" [good people with good people], and he trusts in God. Even with a tough journey, he's still the "mismo chavalito" [same kid] with dreams he's achieved. He's all about his crew, staying out of trouble, and enjoying the good things in life, like being well-dressed and having a "güerita" [blonde girl] by his side. It's clear family is super important to him, as he mentions his family, brothers, and nephew are always on his mind and with him.