I'm planning a visit to the museum in August. The ticketing process for the Age of the Dinosaur exhibition asks you to specify a time when you wish to enter. Do you know if you can re-enter the exhibition more than once on the same day? (I have a 5-year-old, who is likely to want to see the rest of the museum and then come back again to see the dinosaurs).
I would recommend getting to the Museum as close to 10am as you can going to see the newly cleaned and re-opened dinosaur gallery which is off the main hall first as the queues get quite lengthy for that gallery. After the dinosaurs I would pop down to the basement to our Investigate centre where we have real specimens that your son can touch and look at under microscopes. We even have genuine dinosaur things that he can touch. Then I would suggest going to the exhibition. Also I would check the website to see what is on that day as we have a handling trolley called hands on nature that is all about dinosaurs with people working on it who would love to talk to your son about dinosaurs. After all that I think he will be very dino happy indeed. I know that doesn't answer your original question. But just in case you can't re-enter the exhibtion you have plenty of dinosaur options.