Having been born in the US, they are citizens whether they want to be or not, and under US Law and treaties in effect with Canada, they will forever have to report and pay US taxes on their income, even if they never set foot in the US again.
If the US fancies itself as being so liberty-oriented, not to mention fair minded, it must give such children the right to “opt out” of this tax slavery.
Put down the crack pipe... now back away from your keyboard.