Infant Linguists ~ Learning N-Languages as Kids

Why not learn many languages as kids -- especially even as infants, tykes, kindergarteners? Check out these Dutch infant linguists... FYI, I learned both Dutch and English by age 5 and both are still with me -- to some extent;-) But trying to learn Spanish and Japanese as a late teenager was pure torture for me. Still irritates me that I didn't learn a dozen languages as a child -- i.e. English, Chinese, Arabic, Russian, Portuguese, Spanish, French, Swahili for certain. Dutch for family-sake (and maybe so I can harass my Afrikaner friends;-) And then probably Japanese, Korean and German because they're so important as technosavvy countries. And perhaps Italian, because it's so vibrant, and the Scandinavian lingos, if only because the women are so beautiful, and then maybe Latin and Greek, because of their etymological legacy. Probably wouldn't hurt to know a bit of Turkish, Farsi, Hebrew, Urdu, Hindi, Bengali, Malay, and Tagalog. Not sure I can wrap my tongue around Finnish or Khoisan, but I'd try just because the people are so cool! My point is that ALL of those languages are a helluva lot easier to learn when we're kids than as adults. So why does standard educational orthodoxy insist on waiting till kids are 10 years or older to start language classes?