Apparently huge in South America

I have a friend at work who is originally from Uruguay, and somehow we got to talking about childhood memories, and it turns out that we share one - our love of this show!
He says that it was HUGE in South America when he was growing up in the 60s & 70s, and said that as a boy he believed all of the characters (and the actors & actresses playing them) to actually be Hispanic, but could tell that they were dubbed, and was confused as to why they had originally recorded their dialogue in English.
We ended up singing the theme-song together - same tune, different words (his in Spanish, mine in English) - quite loudly, and got some funny looks from our coworkers.