It's so important to follow our gut. If you can, I would suggest sitting in for a day and observing the classroom. It is hard to watch a parent leave when their child is having a hard time transitioning. It is, of course not uncommon and so often they orient themselves very quickly after mom has left. I know we always encourage our parents to empower their children when they leave. Be very positive, "you are going to have a great day, I am so glad you are here, I love you, can't wait for you to tell me about all the great things you do today," Leave with a smile of absolute certainty. You must convey to your child with absolute certainty that all is well.
Give them the courage. Listen to their concerns of course, but not at the door of the classroom. If you are bringing them to school, be certain yourself, that it is a safe place for them. If you can't observe with your child present, arrange a time to observe the classroom when he is not there. At the door of the classroom empower your child, and leave. Some of our parents arrange to call in a few minutes to see how things went. It helps some of our children if an assistant engages them quickly, by inviting them to feed the fish or help with the hamster. Some children just need to come in slowly at their own pace. I always found with my own child, he needed to engage with an assistant or the teacher before he could transition, and I asked if they could help me with this. It helped mine to make my goodbye brief, positive and leave immediately. I used to have a good cry all the way home. It's hard to leave your child when they are so upset. In our classroom the children who struggle with transitions do better with brief goodbyes. If parents linger with worry, and concern, they feel it, and respond accordingly. Those that have a hard time transitioning do well to come on time, or a little early. I know how you feel, the bathroom situation would give me pause too, and then again, there may be more to the story. Follow your heart, and check it out, find a place that you feel safe, where you trust the teachers. I have found over the years that my overall love and trust of the teacher and the assistant made room for errors judgement on their part as well as mine. Each child is a journey for all of us on their path. I wish you the best, hang in there, you will find your right place.