Is that Crawford Notch? I think I've stayed there.
So for your son, I'd do the Flume, the Basin, and Cannon Mountain tram. You might have to carry him a bit for the Flume, but he'll like gorge and all the walkways. Definitely drive to the top of Washington, or consider the Cog Railway.
Echo Lake would be fun, and gives him a chance to swim.
There are two easy 'mountain hikes' there, the north and south Bubble. They are very 'doable' for him. I think that there is a place there where you can get blueberry tea, and blueberry muffins, so that could be a nice break for the wife.
That's what immediately comes to mind, if I think of more I'll PM you.
I love the area. It should be a blast.
