1. Prepare a mobile phone number: if you are a parent, you need to prepare a mobile phone number; If you are an administrator, you need to prepare a mobile phone number and a mobile phone number with a supplementary card.

2. Choose reputable operators: Choose reputable operators, such as China Mobile, China Unicom and China Telecom.

3. Choose a package: choose a package suitable for children and confirm the cost.

4. Electronic signature: Electronic signature is required after package selection is completed.

5. Pick up the secondary card: Pick up the secondary card at the selected operator's store and complete the activation of the secondary card.

Please note that before handling the secondary card, you need to understand the relevant policies and regulations of the operator and confirm the fees and functions of the secondary card.