THAT IS NOT OK!! You poor thing. I totally understand how you are feeling! That is scary.
True story... one summer I was supposed to start babysitting a little boy named Jacob. I had never met him before, just his parents and they were really flaky. He was to be going to summer school and a bus would pick him up and drop him off at my house. He never actually started though. The day he was going to start he just didn't show up. Then a week later there was a school bus parked out in front of my house. I walked out to explain to the driver that the boy never started with me. The bus driver just said "then today is his first day." He handed me a backpack and this sweet little boy named Jacob got off the bus. I was so confused as I watched the bus pull away. I went in and looked up the cell phone number to the mother but was never able to reach her. I didn't know what to do. About two hours after he was dropped off the head of transportation and some big wig from the school board showed up at my door scared to death asking "did a little boy named Jacob get dropped off here?" IT TURNED OUT TO NOT EVEN BE THE SAME JACOB!!! This little boy had zero connection to me. He was a little autistic boy who's parents were going out of their mind!! Pretty soon half the police station showed up and some rather upset parents. The mother cried and cried and hugged me and thanked me. The father was angry and wouldn't even look at me. He was too busy yelling at the transportation and school people. Can't blame him one bit!!
Thankfully this story had a really good ending. I am a good person who has a very kid friendly home. (I did childcare at the time.) But what if I wasn't? They don't have any idea how this boy ended up being dropped off at my house. The driver to the bus he was supposed to ride had told his mother "he wasn't at school today." Can you imagine???
Anyway, I don't mean to scare you with this story, but accidents like that obviously happen. Your little guy needs to be kept safe. If that daycare is unwilling to look out for him I would really start making a fuss. If they are still not willing to accomadate you to keep him safe I would find a place that will. His safety and well being have got to come first. Its outrageous to me that they expect this little four year old to do that alone! Can you talk to some one higher than the diretor? Do they at least stand at the door and watch him walk to and from the bus? This is crazy!
I am so sorry that you are having to deal with this. I hope it all works out for you and you can get some piece of mind.
If you do switch childcare places think of doing some in-home childcare. Call Childcare Resource and Referall. They can hook you up with people who do childcare out of their home. Then the bus can stop right in front of their house. AND a smaller setting may be helpful for him.