24 month old and his emotions

My grandson is 24 months old.  He has a brother that is 6.  I know every child develops differently.  The 24 year old is so tiny.  weighs 21 pounds.  eats good...does not say too much..mom, dad, no...those are not real clear.  I took him to see Sesame Street live over the weekend.  He sat on his moms lap..was interested in the whole show..never took his eyes off the stage.  yet, he never smiled, laughed or even showed a sign of interest.  he can hear because if you talk to him when he is not looking. he turns to listen to you. he is always crying for his mother. always looks sad.  falls all the time...has had tubes put in his ears..

[Bri_1985]

It could be nothing. Like you said all children develop differently. However, you can mention it to his Dr and see what they have to ssy.