Some good advice above, but we have seen many times - especially in the last year, where restaurants were booked up when we tried to get last minute seatings. Even though we arrived early, and were willing to take any time. We've also had several times where we were not seated at our ADR time, despite being there early! More than once we've waited 15 minutes past our time (Mama Melrose, Boma, etc.). Your best bet is to eat lunch at off times, and eat dinner early.
If your toddler gets hungry early, you could always give them a snack and just have them sit with you at dinner.
One thing Disney is great about is that there are colorful details everywhere, so there's always something interesting to see. You can usually get crayons and paper to color while you wait for your food. It's hard to desribe, but there is often ahuge array of colors to see, things that move, etc. And your son wil be stimulated all day. Many kids enjoy meals as a chance to stop for a bit at WDW, unlike at home where going OUT to eat IS the event, and kids are wound up.
Most kids love Rainforest Cafe, esp. older ones, but a toddler might be scared of the rain storm part, or certain animals start making noise and moving near them. (leopard, gorillas)
Characters can also be great, but can be scary for a toddler. Also, if your child is easily distracted from eating, the characters might be a bit much. Great once, but not something I'd choose for every meal, personally, esp. if you don't know how your child will react.
Eateries at the resorts tend to be a little bit quieter, especially mid -day. that can be great for a toddler. Again, eating at slightly off times can help to have a more quiet meal.
We usually choose no more than one sit down per day. That way you have maximum flexibilty the rest of the day. Disney has many fun QS places too. Try Starlight Ray's in Tomorrowland!
Last, if you've got a cell phone handy, and you think it might help to change an ADR time, you can call and see what other options are available - different times or locations (Like dinner at your resort perhaps).