Entrañas literally refers to internal organs or 'innards', but it's often used metaphorically to mean the deepest part of something, or even the womb.
In this song, Leonardo Favio uses it in the line "El hijo de tus entrañas," which translates to "The son of your womb." It's a poetic and intimate way to refer to a child, highlighting the profound connection between mother and child, and adding a layer of emotional depth to the lyrics.
Leonardo Favio's "Mi Amante Niña, Mi Compañera" is a beautiful, intimate declaration of love and devotion. He calls his beloved his "amiga, mi buen amiga" [my friend, my good friend] and "amante niña, mi compañera" [my childlike lover, my companion], showing the deep connection they share. He wants to tell the world what it's like to have her all night, exploring "tus caminos, tu vientre fino, tu piel de seda" [your paths, your slender belly, your silk skin], and seeing "el paisaje de tu pelo sobre mi almohada y tu boca fresca" [the landscape of your hair on my pillow and your fresh mouth]. It's a very sensual and tender image of closeness.
He sees her as the "razón de mi vida, mi fe, toda mi alegría" [reason for my life, my faith, all my joy], and even mentions their child, who has "tus ojos de primavera" [your spring eyes] and "tu risa de campana" [your bell-like laugh]. It's clear she's everything to him. He even asks for understanding if he ever hurts her, like a child who gets jealous. It's a sweet, almost vulnerable admission. He also describes waking up to watch her sleep, stealing a kiss, and feeling almost guilty for being so happy, crying silently for those who suffer. It's a really heartfelt and honest look at profound love and gratitude.