Whilst it is true that teaching a foreign language can be a non-starter (post #2) when resources are not available or teachers are simply not proficient enough to teach it, the benefits of starting young are immense.
Noam Chomsky maintained that the human brain has a built-in language acquisition device, or LAD, that analyzes the parts of speech in the language that a child hears.
He found that this concept applies across cultural differences and relates to many different languages. This is "nativism" and children
have neural circuits that are genetically programmed to acquire language.
In other words, we are built to receive, understand and communicate language and it is mainly opportunity that allows some people to acquire more languages than their own. This obvioulsy does not allow for any skill indicators or difficulty level and there are those amongst us who have a natural ability for languages. The potential is there though in all of us.
In South Africa - where education is at a premium and there are still young people who cannot read and write- language is a huge factor. Although there are many who do not even speak English ( a large immigrant population), many, children especially, speak their home language such as Zulu or Tswana and English and these are not necessarily educated - so their teachers are parents, grandparents and community members. Obviously grammar and the written word escape their level of understanding but it does show that it is certainly possible - and even necessary - to encourage second language learning as young as possible. These children will have other problems to worry about when they enter the school system so even a basic understanding of a second language is beneficial.
Many learners in SA must learn in English (or Afrikaans) because there are not enough qualified teachers to teach all the subjects in their own language, their "mother tongue." There is a drive currently to ensure that children - up to age 12- are taught in their own language as the language of instruction, but it will take years for this to come to fruition. Please bear in mind that there are 11 official languages in SA, although many of the "African" languages are dialects and can be vaguley understood by others.
Sorry to digress but as post#4 refers, English is almost a universal language and, lazy as that makes us, we are at a disadvantage if we don't teach younger children a foreign language.
Factually, the younger a child is, the easier it is to master two or more languages. Many average 3 to 4 year olds in SA can speak English and a second language, often Afrikaans fluently - without mixing their languages and, after nursery rhymes etc, they are far better equipped to learn the second language formally on entering school. The school system includes poetry, short stories and analysis from about age 11 when the basics are already been entrenched.
Children with language difficulties and disorders sometimes display psychological problems due to the fact that we are programmed to receive and understand language and cannot comprehend language deficiencies.
So, yes to middles school and a definite yes to younger than that if possible. It can only contribute to the "Global Village."