Some can overlook that clubs may require that a person can only enter club grounds if they are a member, such as a parent or a guardian. It can be an issue dealing with this, although it is not common.
The simplest method is to determine if non-members need to attend the club regularly while not participating in the club sport. If it is required, then there should be a Non Member option during signup so that you can capture their information and they can register for entry on the club grounds. A possible solution can be a free membership or a small fee that covers your insurance obligations.
It's important to note that you need to be able to identify them (id card) and ensure that they are aware of their restrictions while on club grounds.