sorry my hands are so painful due to my pregancy, hope you do not mind I type in English.
To help your baby to communicate better, you can use sign language accompany with spoken language.
The common sign language you would need is "more", "I want". also teach your child to use finger to point will help him to tell u what he wants.
These videos are from my centre which are done by the therapist and teachers in my work. Feel free to have a look;
https://youtu.be/PYljGJ9bu5M
https://youtu.be/S0jwcIPKKPE
My hands are so painful due to my pregancy, I hope you do not mind I type in English. It's faster for me.
Your child has separation issue and he should learn to be independent. the first few lessons, parents can accompany child if necessary but after I think parents should let the child to be independent at school. So May be mommy and daddy do not stay any longer after saying bye to him at school.
It may not be a good sign that your kid totally cling on you. All children should learn to be independent at school.