I think children should learn another language from grade 1, ie 5 years old. At that age it can be all fun and songs and play-acting. I understand they are very good at the 'immersion' method in Canada, to teach English speaking children French and the other way round. If you can get some decent second language teaching in to children before puberty, they have a good chance of becoming fluent.
Here in Australia there are parents who object to this, saying they should concentrate on English and get that right first, but the truth is, learning a second language does wonders for your English, especially grammar. It also teaches children about other cultures: you can't learn a language without learning about the culture too, and this is a great tool to combat racism and ethnocentric attitudes.
Also, having a second language, or more, is now known to combat dementia: it must be something about the different thought processes involved in thinking in different languages.
As for happiness in education: this is achieved through good teaching, and good planning. History and geography, English literature, foreign languages, sciences, maths, etc can all be extremely interesting to learn, especially with modern teaching aids. I still remember my first fortnight of Latin at age 12. The teacher simply told us tales of ancient Rome, of life there, of battles, of the Romans in Britain - I was spellbound. Then he started teaching the language - Latin is very hard but we enjoyed it - well most of us anyway.