Hello, Osana! Welcome to planDisney. I'm so glad you've stopped by to ask your question here.
Osana, I personally have enjoyed both
Disney's Pop Century Resort and
Disney's Art of Animation's Little Mermaid rooms before. They are both fun resorts to stay at. However, both rooms can be fairly small. The square footage of the Little Mermaid rooms is about 277 square feet and the square footage of the rooms at Disney's Pop Century Resort is about 260. So with you making the switch over to Disney's Art of Animation, your room is going to be a little bit bigger.
The resorts at Walt Disney World are broken down into three categories - Value, Moderate and Deluxe. The higher the category, the more space you will find in the room. Disney's Art of Animation actually provides the most space in the room in the value category, so it was a good switch.
If you wanted to upgrade your resort to another category, I would look into
Disney's Caribbean Beach Resort. Disney's Caribbean Beach Resort is in the moderate category and one of my favorite resorts. The rooms here always feel spacious and offer about 340 square feet of living space. Also, the grounds of the resort are beautifully kept and spread out. Nothing feels on top of each other at this resort which might also be great for your son. There are white sandy beaches and calypso music which is so relaxing while walking around. It's such a great place to stay that really does transport you to the Caribbean islands.
I hope this helps, Osana. I know that whichever you choose will be perfect for your son and you are going to make magical memories that will last a lifetime. If you have any other questions, please feel free to stop back by and
ask me. I'm happy to help!