I think you can do it IF you do ONLY the things on your plan and that you do EMH at MK. MK will be the limiting factor - since you want to do "everything" in Fantasyland and Tomorrowland. The other factor will be transportation. Will you have your own car, or will you have to depend on monorails and buses? That can make a difference, too. Not to mention meals!
Since it's your 5 year old's idea, it will be easier than if it's your idea! But you need to talk to him in advance, because you will not be able to do anything but what you've listed, so if he sees another attraction he wants to ride, he needs to know he'll have to skip it!
Also, travel light, preferably no bags to inspect so you can go through security quickly!
We've done at least 3 parks in one day, when we were checking out, to boot, so it's doable. You just have to have a plan and stick to it!