As-salamu alaykum,

I am sorry to hear about the problem you are having with your little boy. Often children will use the mode of communication which gets the best and fastest results! Apparently, he has discovered that crying brings the quickest response.

 
I would kindly suggest that when he begins to cry, ask him “what”? Ask him to verbalize “tell me what?”. If he continues to cry, prompt him by saying “drink”? If he nods tell him “say “drink” . If he says “drink” (or whatever the case may be) then give him the drink. If he continues to cry, withhold the drink until he verbalizes what he wants.
This will take much persistence, consistency and lots of patience on your part but it will be worth it in the long run. Once your son gets use to the idea that crying will not bring him results but talking will, insha’Allah you will see a decrease in the crying and an increase in his verbal responses.

 
As long as your son is healthy, not hurting or sick, there is nothing wrong with letting him cry or scream for a few minutes. You will need to do this, to let him scream and cry in order to train him up in a proper manner. Once he re-learns how to communicate this should cease. It is my feeling that he is a very loved little guy who just got use to getting whatever he wanted by just a cry, whimper or scream since he was very tiny. Now that he is older, it has intensified and will take some work on your part (and the family) to undo this unsavory habit. Insha’Allah, in time a sweet little boy will emerge who asks and communicates his needs through more appropriate measures.

 

We wish you the best, you are in out prayers.