Non verbal Preschooler

I am not really sure what I am looking for here.. maybe just some solidarity. My baby starts preschool Monday. He has a diagnosed receptive / expressive speech delay. At this point in time he has no communication skills. He is in speech through our local hospital and will receive it through school also. We see a developmental pediatrician on the 9th, hoping for some answers on how I can help him more. I’m limited on what I can do to make sure my baby is being treated right in school, I am really going through it mentally worrying about him. I know I will always worry, but that extra layer of worry when your child can’t verbally communicate things to you. Do I just watch his personality? Make sure I am paying attention to his body language and how he acts when coming home and going to school? I want to protect my baby boy as much as I can. I just can’t stop worrying myself sick.. please send some encouraging words.