You may have made a minor incorrect assumption Muchjo, kids learn languages easier than adults if taught soon enough , would it not be more correct to say "easy for all ADULTS to learn" as I see that the major point of resistance...
Actually, that's false. There is plenty of research (vz. Frank, Formaggio, Ur, etc.) that have proven that on an hour by hour basis, adults and older children learn a second language faster than younger children do. There is general consensus among researchers that for difficult languages, it's best to start at the age of ten, and for easier languages, eight.
The reason for the myth that younger children learn faster is owing to the apparent ease with which they learn their mother-tongue. This ease is only apparent and not real, however. In fact, children find it more difficult to learn their mother-tongue than a second language. The reason it appears easier is as follows:
1. Adults remember how hard it was to learn their second-language, but not their first since they wre too young then.
2. Young children are exposed to the mother-tongue around 12 hours per day, and everyone is their teacher, including teachers, parents, TV, radio, music, bus drivers, waiters, etc. etc. etc.
3. The survival motive. The child has no choice but to learn his second-language to communicate basic needs to his parents.
Try to reproduce this in a class-room setting, and it's been proven in European elementary schools to be utterly impossible. Overall, it's agreed that in a classroom setting, younger children learn a second-language very poorly and inefficiently. In short, it's a waste of time and money unless the parents know the language too or they live in a community that uses the language, etc. Otherwise, if it's all to be taught in the classroom, good luck.
As for adults and older children, they understand the grammar of their mother-tongue already, so the teacher and students can exploit that to their own advantage to learn the second-language more quickly and easily than they'd lernt the first. The only reason they seldom learn the second-language as well is owing to the time investment and exposure received compared to the first. But if you teach a young child a second-language and an adult or older child the same scond language over the course of an hour in a classroom setting, the older child or adult would beat the younger child hands down.