Poultry Talk Ontario (pto.ca)

Hmm, curious. It could be because they are Cal Val quail. I don't have any experience with other types of quail other than Coturnix. It could well be that they need a bit of extra time to figure out the whole dust bathing thing, since they are only three weeks old. You could try sprinkling songbird seeds on your sandbox, or maybe meal worms ... whatever they consider special treats.
Patience, observation and "necessity is the mother of invention" will go a long way.

Just to update. I put sand in the coffee can lid I feed them in. All sand gone this morning!
They are so afraid of new things. The sand was just in a Pile on floor. ?? Wooooooowoooo scary I guess