The section to request really depends on what's important to you. Right now, you may hear a lot of people say they prefer not to be in the Paddocks and especially not the Carrousel. That's because there's not a whole lot going on in these sections. However, if you're visit is after mid-summer, the new Paddock pool complex will be open. This has a new feature pool (with slide) and a quick service restaurant. I think these two sections will find a lot more demand with the opening of the new pool.
If you want to be closest to DTD, Congress Park should be your first request. This section also has it's own quiet pool.
The Springs is closest to the main theme pool, the High Rocks Springs pool. It's also closest to the Carriage House, where the restaurants, shops, and front desk are located.
For a 3 year old, you may want to consider the Grandstand section. The pool complex there has a water play area that's great for kids of that age.
lol, so there you are. I've recommended every section of the resort except the tree houses to you. Those are wonderful, too.
Every section has it's own bus stop, although there are buildings within each section that are closer and farther away from the bus stop. If that's important to you, add a request to be "near bus."