The Search for the Perfect Language. Which language would children use?

I always remember Jim Carrey, in his movie Fun with Dick and Jane, when he is trying to explain to the immigration officers that he is an American citizen, not a Mexican, and he has lost his documents. And when they call home, his son, answers in a perfect Spanish learnt from the maid. That was really funny, he never expected the boy to answer in another language different than English.  
But children learn languages so quick, and for bilingual people, there´s always the discussion on which language has to be spoken at home. Leave a child without restraints and he will speak all the languages he listens to every day, he will mix them in his universal language.
To learn much more on this subject, we should read Umberto Eco:¨.... this multiplicity is a wound that must be healed by the quest for a perfect language. Before one decides to seek a perfect language, one needs, at the very least, to be persuaded that one´s own is not so.¨ (p. 10). In his book The Search for the Perfect Language, he explores the origins of language, the one that could define the essence of all things; after all, God said ¨Let there be light¨, thus, Creation -he says- arose through an act of speech. He bases his research on arcane treatises and relates the language to identity.
As a reflection, I´d like to share these words cited by Umberto Eco, after the Preface:
(Frederick II) wanted to discover which language and idiom children would use, on reaching adolescence, if they had never had the opportunity to speak to anyone. So he gave orders to the wet nurses and to the feeders to give the infants milk, prohibiting their talking to them. He wanted to find out whether the children would speak Hebrew, which was the first language, or else Greek or Latin or Arabic, or indeed if they did not always speak the language of their natural parents. But the experiment came to nothing, because all the babies or infants died.

Salimbene da Parma, Cronaca, 1664.