The mathematicians of the future will still have to figure out the right questions, even if llms can give them the answers. And "prompt engineering" will require mathematical skills, at the very least.

Evaluating the output of llms will also require mathematical skills.

But I'd go further, if your son enjoys mathematics and has some ability in the area, it's wonderful for your inner life. Anyone who becomes sufficiently interested in anything will rediscover mathematics lurking at the bottom.