As to "do you need" ADRs, they are a safety net. In September, we had a night with no ADRs, no dining plan. I called Disney Dining and was told that the 3 restaurants I named were full. DD really wanted Chef Mickey's, so we went over and were seated in less than 5 minutes! However, we timed it right because as we were leaving, there was a long line waiting to check in.
This morning, I called and changed one of our ADRs for May--got exactly what I wanted.
So...yes, you can wing it without ADRs, but you are taking a huge chance of long lines and not eating where you want. Some of the DTD restaurants take ADRs, some are "walk up." Again, ADRs are a good idea.
I plan on what parks we are going to on which days, then pick a restaurant in or near that park. We do CD lunches, TS dinners...you may have other preferences.
All Ears has the restaurants arranged by location (which park or resort they are in). Dis world site does this also, and you can also look them up by type (character dining, etc)
At MK, our favorite is Liberty Tree Tavern (characters, served family style.)
At MGM, your son might enjoy the Sci-Fi Diner--you sit in cars to eat and watch movies (yes, there are tables built into the cars). There is a new Character restaurant supposed to open in MGM this summer with a Toy Story theme. Target date was posted as June 1, but since this is after our trip, I really haven't kept track of whether or not this is accurate.
Epcot--Garden Grill (characters). Any huge number of international restaurants.
At the resorts--Chef Mickey's in the Contemporary (a short monorail ride from MK), 1900 Park Fare in the GF (great food...same deal on the monorail.)
At Beach Club--Beaches and Cream has great hamburgers and ice cream desserts. Whispering Canyon at Wilderness Lodge--lots of fun.
That should give you somewhere to start.....any place at WDW is "kid friendly", but some are more kid oriented than others.