To me, it is a serious problem if there is someone "keep" pushing / hitting your son at school. And if this is the reason to make your son refusing schooling, it have to be resolved as soon as possible.
It is because the teacher should have the responsiblity to watch over the kids. To teach and report the above to you. Have you ever called and asked the teacher about the case? What is the response of the teacher?
You know what, in order to let your son have a happy schooling, this matter MUST be solved.
Or at the worst case, transfer to another kinder can be considered.
one of the K1 students in my son's school is also like this, his mum told me that for the last 1 year, he always cried not going to school, and struggled at the school door. But he was OK during the school time. His mother found no particular reason for his dislike for school, she thinks that it is because he is still small, cannot enjoy school life yet. But in recent few days, the boy seems better, no crying. His mum said he was a little bit better, and he didn't cry because his mum allowed him to bring some toys to school for sharing.
If your son has no serious problem at school and you trust the teachers, maybe one of the choices is: accept your son's dislike for school but send him there just the same.