Well my brother in the Force, you've come to the right place. Join me, as I tell you how to slaughter not just the men, but the women and the children too! That way, you'll finally be able to complete Order 66, and bring peace, freedom, justice and security to your new Empire.

You can't. For some reason, they're completely invulnerable to friendly-fire damage. You can still beat the ever-loving sand out of them, as well as kill them in the Complete Saga, but it's just not the same.

TT Games didn't consider the NPCs though, or at least the free-roaming ones. They're still invincible if they have dialogue, but otherwise you can freely dismember them to your heart's desires. The easiest method to find these younglings is to enter the Jedi Temple on Coruscant's Federal District.

You can't kill specific younglings like Anakin and Boba Fett, but NPCs without dialogue are a-ok. Good luck, and may the Force be with you.