To use the Set Up Safe service, SET UP SAFE to 150. You must be the account holder.
Controls & Settings guide
EE’s Set Up Safe service helps to keep your children safe online by providing age-specific packages to block adult content, set spending caps, and stop them adding extra charges to your bill. There are three packages which range from under 9s, 10-12s and over 13s.
The Child's device, an EE account (Email address and Password) and you must be account holder to make changes
Here are more resources to help you keep your child safe online.