Most real events aren't a single door at a single time. A fair has talks, a training day has streams, a launch has a morning and an afternoon. Set those up as child events and each guest tells you which one they're coming to as they register.
The parent is the thing people say they're attending. The children are the parts they actually turn up to.
Instead of one attendance number, you see which session pulled a crowd and which one didn't — before you plan next year.
Registrations per session tell you how many chairs, how much catering, and how many staff each part actually needs.
Guests choose their session on the form, so you don't have to print and distribute a separate code per session.
A guest's pass is tied to the session they chose, so when they scan at the door the attendance is recorded against that child event — not just against the fair in general. The participant list shows it that way too.
Tell us the sessions and timings and we'll set the parent and children up so the registration form asks the right question.