The key to the club is that the child needs to be able to handle ALL bathroom needs. That means without help from counsellors. It is more than "can tell them when he/she needs to go." However, the way to mitigate this is for you to go to the club every 90 minutes or so, just to check in. Take your child to the bathroom while you are there.
Many kids are "potty trained" to the point that they can tell you when they need to go, but may still need help with clothing, wiping, etc. These are the things that the counsellors specifically are not to do. It's an unfortunate reflection of our society, but bottom line is that they cannot go into the restroom with the child. In the event of an accident, they will help the child clean up and page you. The easiest way around the whole issue is to show up yourself periodically and take the child while you are there.
The activities there are really great! Most little ones love it.