You won't find coupons for any of their restaurants but they do offer a discount meal ticket you can purchase which will save you, an adult, quite a bit of money. Many of the meals could be shared with your son plus you get one of their refillable cups with the meal ticket which you can refill for free with water all day. Soda refills are .99. Guest Services just inside the park sells them - I think they are $12.95 this year (the cup alone is $7.95)
Definitely make the trip to ZooAmerica (which is attached to the park and included in your admission.) My small children enjoy the animals - especially the prairie dogs and the bears.
Try to do the Hershey Factory Tour ride in Chocolate World as well, my little ones like this a lot because of the singing cows.
There are lots of opportunities to feed ducks so take a few quarters along for corn. My little ones love this too - and the sea lion show in the Aquatheatre.
Hershey is my home park and it is great for kids. Have fun!
They will give him an official measurement and then give him a corresponding wristband that shows his height category. This saves you tons of time in lines since he won't have to be measured every time. Well worth the few minutes if you have a child who is close to a height cut off.
(The height measurement area is also a great place to take a picture if you will come back to Hersheypark often. I started taking pics of my daughter when she was just a miniature and it is interesting to see how she has grown and moved up in the ranking until now she is way past the highest one.)
You can do a family finder ID band at Hospitality Services as well. Park Security will give your son a wristband with your cell phone number on it so that if he gets lost you can easily be contacted.
Walt Disney World's Magic Kingdom
Disney's Animal Kingdom
Disney's Hollywood Studios
Disney California Adventure
Universal Studios Florida
Universal's Islands of Adventure
Universal Studios Hollywood