Need help with toddler behavior / early intervention

My sons daycare has called me and told me he is not adjusting to the toddler room.

Basically the class is 18months to 2.5.

My son is 20 months to be exact. Most of the kids are 2 already

He just moved up into the class at 19 months old

They feel he isn’t adjusting. He isn’t speaking a lot. He only says few words most of his words are gibberish. But he understands when you tell him to do something..and he knows shapes and colors he does all the puzzles and toys he just doesn’t say what they are except “blue”

I’ve expressed the talking with my pediatrician and they said he isn’t even 2 yet and not to worry.

Now the new part which I did not know about is that he will hit the kids or teacher in the class for them to pay attention to him. And cannot sit for few mins in circle time. So they’re saying he either needs a behavioral specialist or some type of early intervention

He does not hit my husband or myself or any of his cousins or our friends kids so this is new to me....

I feel he’s still kinda young. I just called back my dr office to talk to them again. He’s a very happy kid so I’m caught off guard

Anyone deal with this on a kid under 2??