We had massive rows about the issue of CRB checks and child protection policies in the club. In the end, we ignored it, however some of the instructors decided they wouldn't fly with Youngsters unless there was another adult present, such as a parent. Obviously that can cause problems if you only have 2 seaters available.
Having a CRB check for your normal job (if a part-timer) doesn't count. You need a new check for a different job...
It's utter madness, but like any of these things, this is just an ar*e covering excercise, rather than something that actually makes it safer for "vulnerable" people.
You should be covered by the club's liability insurance as you are working for them, no matter what your actual employment status. However, you might want to make sure that they are actually covered! I have found more than one school that has been lax with things like that.