There are really three options:

1. Give away your money after you make it.

2. Give away your money as you make it.

3. Stop making money once you've earned enough of it.

Elon has chosen #1, and that is a viable option. It's viable because fortune begets fortune, and if he'd chosen #2 (or certainly #3) he might not have been able to create as much wealth.

That fact that he's not choosing to set his children up for life (apart from, I'd imagine, enough to get them through grad school comfortably) is to his credit and to their ultimate benefit.