concern for a friend's child?

[Frank]

our friend's child was 2 back in May...he has no words as of yet...not even Mama or Dada...he seems to understand everything we are saying though....he SCREAMS when he wants something...really piercing screams....he didn't walk until he was 18 months (or more)...and even then was really unsteady until recently....he flapped his hands very often and waves really strangely...also, you couldn't let him anywhere near another baby cause he'd just come whack off the baby's face....his mum has taken him to the doc and they seem to think he's ok...the rest of us aren't so sure...what do you all think?
he is an only child (at present) - although not for much longer....and he was born by elective C-Section at 39 weeks.