Decide whose account it is

Every phone signs in to an Apple ID or a Google account. Which one goes on your child's phone shapes everything after it, so decide before you set anything up.

Do it

1. Pick the account. Most families make a child account. On iPhone, set one up through Family Sharing. On Android, through Google Family Link. Under-13s need a parent to create it.
2. Write down the password somewhere safe. You'll need it for Step 5.
3. Keep your own password to yourself. If a child knows the password for the Apple ID that set up Screen Time controls, they can switch those controls off in Settings.

Why now

Changing the account later means signing out, losing app data and setting things up again. Five minutes of deciding today saves an evening in January.

More on this: iOS setup guide.