I don't have any kids who are studying law, but I could offer some opinions here.
Having a marketable (that is, something that allows your child to have a decent career) bachelor/master/PhD degree is desirable, not for the reason that you cited, but to have something to fall back on if he/she could not get a job at a law firm after he/she finishes the law study. For instance, having an Engineering, pharmacy, chemistry, etc.
Also, it seems now that having a bachelor degree is not enough as law practicing is quite specialized. Having a PhD is ideal, I believe.