Unsafe indoor play area

Took my son and his cousin to this "safe" indoor play area. Everything looked fine at first. After about an half an hour my son go lost. None of the childminders (4 in total for about 20 toddlers that time) even gave attention to help me look for my son. The exact words from one of the ladies when I asked her if she seen my 2 year old boy, was "ah theres no children here". After about 15min we found my son in the upstairs area where a party was being held. He had to climb up a flight of stairs with glass banisters. I literally took one bite of my food and he was gone out of sight. How did no childminder see this baby climbing up the stairs? The manager told me that this happens quite often. The stairs isn't safe at all for todlers. Why don't they put gates at the top and bottom that adults can open? The food was awful. My husband had a cheese burger, the top of the bun looked squashed by a todler. Only half of the burger had a piece of patty on. All staff was required to help set up for another party coming in. Please be careful if you do go there.