My 19 month old grandson used to babble, now he just grunts and makes an ehhh sound. He understands everything, points knows letters & numbers.?

Change in infant sou. You can observe for few days and if you feel he is not doing what he was doing before, have him be examined by your pediatrician, and see if there is a problem.
Abnormal. By 19 months of age the kid should have recognizable words he uses for people and a few objects. All infants, including those with significant speech and language problems understand more words than they use. Time for a hearing and speech screening.