"Demeny voting is the provision of a
political voice for
children by allowing
parents or
guardians to vote on their behalf. The term was coined by
Warren C. Sanderson in 2007.
[1] Under a Demeny
voting system, each parent would cast a
proxy vote, worth half a vote, for each of their
dependent children, thus allowing for a split vote if the parents' political views differ. Once children reach the minimum
voting age, their parents would no longer vote on their behalf."
https://en.wikipedia.org/wiki/Demeny_voting
AFAIK no jurisdiction in the US has experimented with it, and arguably it would be a violation of one-person-one-vote, because it is *not* the equivalent of giving children the vote; the interests of parents and their children are not necessarily identical. (An analogy: Suppose that in the era before women got the vote, each married men was given an extra vote to "represent" his wife.)
But what other countries might adopt it? (As the article notes, it has been advocated in countries with a large aging population like Japan in order to combat "gerontocracy.")