Do children need a bus card to travel to Beijing? Is it okay to share one with adults?

If children are too tall to buy tickets, they can use a card. The subway must have one card for each person. Without a card, they can buy tickets on the spot. It can't be used by two people, because the same card will be swiped once when entering the station and once when leaving the station, and the fee will be deducted when leaving the station.

The bus one-vote system can be used, but every other person has to brush it for the second time. It is not a one-vote system, or it is not charged by mileage, and getting on and off is also a brush.