Hi Katie!
How exciting that you're planning your family's very first Walt Disney World vacation!
With your youngest son being only 2 years of age at the time of travel, you'll find that the reservation system will allow you to quote & book any standard room that usually sleeps four guests and you will be able to request that a Pack 'n Play be added to your room for your toddler to sleep in.
This request can be accommodated at any Value or Moderate resort,
Another option to consider, if it interests you, without requiring a suite, is
Disney's Port Orleans Riverside Resort. At this beautiful, riverside resort, you are able to book in the Alligator Bayou section of the resort and reserve a room that sleeps 5 via a pull-down wall bed. This may be a great option for you to consider as well if your two year old would be more comfy in a regular bed snuggled with his sister and your five year old could then use the 'child-size' pull down single bed. The bed tucks away neatly during daytime hours.
I hope you'll visit again soon if there's anything further I can assist you with.
Have a Magical time as you plan for your family's vacation of a lifetime Katie!
Kirsten