I would get either the Unofficial guide to Disney World or Birnbaum's guide to DisneyWorld, and scan through the descriptions of Animal World (since you will be so close), Magic Kingdom and Hollywood Hollywood Studios. (I left out Epcot, because your child will probably prefer the other parks more, but it doesn't hurt to check.) Then go back through and try to figure out what you think your son will like, and make a list of those things, and try to prioritize what you would like to do. You might want to also do this for what you and your husband would like, but trust me, a grouchy kid makes for a lousy day, so I would concentrate on your son.
Once you have figured out what you would like to see if you had enough time to do everything, take a look at your top priorities, and see which park they are in. If your child loves animals and dinosaurs, you will need a day in Animal Kingdom. If he likes Star Wars, you will need at least part of day in Hollywood Studios. Then you can decide which parks you want to go to. You may want a park hopper for one day to see those things.
Some rides are more popular than others. If you want to see one of those, look to see if Fast Passes (
https://disneyworld.disney.go.com/faq/fast-pass-plus/product-description/) are available, or put them on your list to do early in the day. You may want to consider skipping some things that have notorious long waits, especially since your time is so limited.
There are websites and smart phone apps that can put together a touring plan for you based on your list, and if you think your child won't mind a fast paced day, it might be worth it. But another strategy is to figure out 6-8 things to do during a day, and if you get an opportunity to do more - Yippee!
Getting to the park as early as you can manage is going to help you immensely. There will be a crowd prior to opening, waiting to see the rope drop. I always aimed to get to the park 10-20 minutes after opening, so that we would miss that crowd. If you are doing a character breakfast in the park, you can start off your day that way, and possibly get into the park early if you have the first reservation time in the morning.
If you have a smart phone, download an app that has the wait times for WDW for the different parks. I like Disney World Magic GUide, because it has maps, park hours, Wait times AND Dining (descriptions and menus of all the restaurants).