The prepositions changes with the meaning of the verb. Salir de means exit or go out, while salir para means go to. For example, Yo salgo de casa / El bus sale para Madrid en cinco minutos. In thencase with regresar, "a" is used with phisycal places like home, and "de"with non-physical places, like holidays. And you are right, le is referring to "el niño", it is just emphasizing the indirect object. It is usual in Spain with some verbs.