To memorize something, it include two step: intake of information, and mobilization of this information.

So anki help to write into memory, expose to new things eventually, and associate two ideas. But the more there is association to ideas, to different contexts, the better.

I think kids benefit from Anki, it's not as different as a puzzle game, but side activities are as important as anki.

I think teaching kid all countries of the world might not be necessary, it might vanish if not used. But it's definitly not harmfull.