I'd tried to (in HF19 time) but it won't let me bring the "child account" below 1.0 SP.

And anyway I may not want to - just in case the person I gifted an account to changes his/her mind and gets back and tries to post or comment or upvote, I would certainly no want him/her to not be able to because I've stripped the account of all SP.

I tested in the past and with 1 SP one could still do something under HF19. Under HF20 that doesn't seem to be sufficient anymore (I need to test again) so I left 3 SP to each of my "steem children-in-law"