Aquí os dejo un libro super interesante sobre este tema y una artículo sobre la edad ideal para aprender un segundo idioma:
"Consigue que tu hijo sea bilingüe" de Barbara Zurer. Lo puedes encontrar en inglés y en español.
http://www.casadellibro.com/libro-consigue-que-tu-hijo-sea-bilingue/9788492968053/1776102
It's never too late – or too early – to introduce your child to a second language.
"Learning a second language is easier for children under 10, and even easier for children under 5, compared with the much greater effort it takes adults," says Pearson.
The optimal time, according to experts, seems to be from birth to 3 years – exactly when a child is learning his first language, and his mind is still open and flexible.
The next best time for learning a second language appears to be when kids are between 4 and 7 years old, because they can still process multiple languages on parallel paths. In other words, they build a second language system alongside the first and learn to speak both languages like a native.
If your child is older than 7 and you've been thinking about raising him bilingual, it's still not too late. The third best time for learning a second language is from about age 8 to puberty. After puberty, studies show, new languages are stored in a separate area of the brain, so children have to translate or go through their native language as a path to the new language.
"We hear so much about the special 'window of opportunity' for young children to learn two languages that it can be discouraging to the older child," says Pearson. "It's true that it's easier to start earlier, but people can learn a second language even after the window has closed."
es un libro ácido, humor inglés, una historia bastante divertida. 
es un libro más serio, me gustó mucho porque muestra algunas de las paradojas de la vida con gran maestría y sencillez. Más info aquí:
otro libro del mismo autor, se nota que me gusta. Este libro cuenta la plena y larga vida de una mujer que vivió como ella quiso, dejando algo de lugar también para el misterio. Una lectura amable que es posible que guste más a mujeres que a hombres. Más info: