Off the top…
Settings > Screen Time > [name] > Content & Privacy Restrictions > Location Services > On
Settings > Screen Time > [name] > Content & Privacy Restrictions > Don’t Allow Changes
Settings > Screen Time > [name] > Content & Privacy Restrictions > Account Changes > Don't Allow
If your child is disinclined to cooperate, your tracking efforts will fail. The iPhone could well be “lost”, “misplaced”, “left behind”, “borrowed by a friend”, “battery-depleted”, or Faraday-bagged, among various other responses.
All of parental controls and all related efforts can be bypassed, and on an allowance-scale budget.
Your child has agency.