Scuba, one thing you don't mention in your first post is if you are planning on finding a club and an instuctor to help you learn or if you plan to "got it alone" with your son. The reason I ask, and most will concurr, is that first plane choice is going to be dependent on if you are going to learn with an instructor or just plan to learn to fly with you and your son and the plane. If you plan to "buddybox" with an instructor, then the planes you have been advised to get are all good ones, although for the life of me I don't understand why you would want to go fuel when electric is so much easier and less messy.

If you plan to go it alone, then I would recommend these planes:

Hobbyzone Super Cub
Flyzone Sensei
Parkzone Apprentice
Hobbyzone Firebird Stratos
Ares Gamma 370

The HZ Super Cub is a 3 channel trainer with no ailerons, but is a pleasure to fly. This plane will probably give you the greatest chance at success. You could also augment this plane with a Hobbyzone Champ, but the Champ can only be flown in windless conditions for optimal results. The Champ is basically a micro version of the HZ Super Cub.

The FZ Sensei and PZ Apprentice are 4 channel foam trainers with a great following and I have heard many instructors endorse them.
The HZ Firebird Stratos is a very beginner friendly plane with a unique stabalization system that actually works as advertised. The downside to this plane is it has a proprietary TX and cannot be bound to any other TXs.

The Ares Gamma 370 is a little bit smaller than the HZ Super Cub but is essentially a 3 channel high wing trainer very similar to the Super Cub. The upside to this plane is that Ares markets a 4 channel "aileron" wing and brushless motor system for the Gamma 370 and both are essentially bolt on accessories. This plaen is designed for the pilot that has advanced from a 3 channel to a 4channel trainer.

Hope this helps and good luck.