The rule for voting is very simple: if you are legally allowed to make decisions for yourself, you are allowed to vote (with a minor exception of certain kinds

The rule for voting is very simple: if you are legally allowed to make decisions for yourself, you are allowed to vote (with a minor exception of certain kinds of criminal convictions). Children and people who are mentally impaired to a severe degree are not allowed to make legal decisions, and are thus not allowed to vote. What you're proposing is nothing but an absurd over-representation for parents of small children, who will be able to vote twice or even more.