Honestly I would have left already if I was told by people who worked there that it wasn't a good centre.

Trust your instincts. Because the consequences are too high if there is something going wrong.
My ds didnt get his bottle at daycare the other day but they went through it with me because he refused it. He had refused his bottle that morning too so it was probably just due to teething. But the point is that they explained what had happened.
But also I think you should ask the carers (nicely) point blank what happened as it is a lot easier to tell how sincere they are then if you go to the director and she gets their story and tells you second hand. Plus it lets them know that you notice these things and they might pull up their socks.

Good luck!