To expand and agree: turnips, beets, hard whole grains, if their baby teeth aren't visibly worn by the time they fall out, it wasn't hard enough.

Jaw and face bone grows by stimulation. It's not just a dental thing - it's sleep apnea, sinus infections, facial structure, voice timbre, and attractiveness.

If it's enough, they won't even need their wisdom teeth pulled - having your wisdom teeth pulled is substantially a standard american diet issue, not a human genetic issue.