In fairness to the kid actor (Nino Del Arco, uncredited, according to the IMDb), it wasn't necessarily his performance that was so bad ... it was the performance of whoever was dubbing him into English.
Another actor who deserves a mention, I think, is Margarita Lozano as Consuelo Baxter. I often wish we knew just a bit more about her. Why did she marry Baxter, the American intruder, in the first place?