Lambchops don't worry, my dad was the same on his first visit there - had never been too far afield previously and loved it. One thing to consider is that it'll be very humid which might tire him out a bit, hat to cover the head is a good idea (baseball cap US-style!)
Definitely recommend a trip out Ellis Island.
Also, for the open top bus tour you can buy a ticket with a multiple day duration - you won't cover everything in one day and nice not to feel rushed.
The Rockefeller centre is less packed than the Empire State - head up to Top of the Rock for amazing views and also there is a guide in advance which was very interesting re the Rockefeller family, background in NY etc.
If you have the energy a walk over the Brooklyn bridge is worthwhile, you can get off the bus tour there, stroll over and look back over the island of Manhattan
Staten Island ferry
Stroll around Greenwich village, Little Italy, Chinatown - you could spend a day wandering around there, plenty of little coffee shops, book shops and restaurants to while away the time and watch the world go by. The buzz and energy of NY is what I think parents really enjoy.