As a mother raising bilingual children I couldn’t agree more with that statement. A second language should be though just like the 1st, by listening and not by doing grammar exercise. Also, don’t wait until middle/high school to introduce a second language, is never too early to start. Find a way to incorporate the new language into your life, I suggest using the vocabulary just learn in context with the rest of the sentence in your native language, that way you get to practice that one or two word through out the day and before you now it the vocabulary will grow to full sentences.
And example of my suggestion is if you learn the word table in Spanish “mesa” then you can tell to your kid to: get your books from the “mesa” before dinner. Hope someone finds this helpful.