Inconsistent and bad attitude

I went to the gym on the 7 January 2016 with my sister who is 16, she was not going to gym just watch as she was in my care and I didn't want to miss out on my gym session. The gym would not allow her in to just sit and watch but I have seen young children at the gym previously that have been allowed in and these children play on the machines and gym equipment. This is very inconsistent, it dangerous to have children playing on the equipment which the gym does nothing about but I had to miss out on a gym session as a paying customer because the gym would not allow my responsible 16 year old sister in. I take care of my sister regularly, this will not be convenient for me as I will now not be able to attend the gym. Very annoyed with the service and attitude of the staff at Virgin Active Sunward Park