You go through the same process as you did when you got your son set up on 48 except that you need to use a different email address for a separate My48 account.
Unlike some other providers 48 don't support group/family accounts where multiple SIMs can be managed under one My48 account login.
Every 48 SIM needs a different My48 account and email address.
See the New to 48 FAQs.
If you need to contact 48 support about this then see the links in my signature below.
