Purchase approvals for children in a game store

Your company runs an online store for games and add-ons on consoles and phones. A child under 13 has an account inside a family, with 1 or 2 parents. A child cannot buy anything without a parent's OK.

Today a parent types their own password on the child's device to allow a purchase. Many children have watched them type it. In the new flow, the child taps Buy, and every parent in the family gets a request on their own phone. It shows the item and its price. A parent taps Approve or Decline. The family's card is charged once a parent approves.

A request that no parent answers within 24 hours ends. Prices change often during sales. The store has 2 million families with children's accounts, and children send about 300,000 requests a day.

What do you store for a request, and what does the server check when a parent taps Approve?