LOL, 20lbs in 3-4 years? Are your kids actually lifting weights. I put on 96lbs in highschool naturally. Not all lean mass of course, but significanlty muscle as I graduated at 17 % bodyfat. Also why have a highschool kid waste money on something like Nitric Oxide.
To the poster, protein and tones of BCAA's. Also, at 18, what does your doctors growth chart evaluation say about how tall you will get, are you expecting to get significantly taller. Depending on genetics you may be, for the most part, done growing.