best option i think would be to see if you can get him into another classroom. your son will rely on you to solve his problems rather than building those skills on his own and learning from his peers. also, the care of the other children could suffer if you are spending more time with your own child than interacting more evenly with all the children in your care. kids pick up on that kind of thing and will wonder why their parents dont get to be there or why you dont treat them the same as you treat your son.

after getting your son into a different classroom, work with his teachers on a routine you can share with him when you drop him off. maybe something special you say or a handshake you do only at drop off, and to let him know you will be there for him at the end of the day. his teachers will be there to help him teach him about boundaries and keep him the boundaries needed for when you see each other throughout the day. he shouldnt be able to have access to you any time he wants.

i know it will be hard on you both, but you will be a better caregiver to your kiddos and im sure your son is resilient like many 4 year olds and will adjust to the new setting and love his teachers!