English: My son
Meaning: Actually ‘mijo’ is not so much slang as a contraction of the words ‘mi’ and ‘hijo’: my son. However it is often used not only with one’s own son but in a friendly way to any boy.
Muchacho: “¿Quiere que le ayude con sus compras, señora?” Doña Hortensia: “Sí, mijo, gracias.” (Boy: “Would you like help with your purchases, ma’am?” Doña Hortensia: “Yes, son. Thank you.”)