I found the recipe for the frosting and the way to cut the graham crackers online, and assembled the house bases an hour or two ahead of time. This turned out to be a good idea so they were nice and solid when the kids added all the extra weight of the candy.
Here are the four kids' houses. My oldest had to add a few more levels and bump-outs to his house.
And finally, the littlest enjoyed the first bite of his house after waiting patiently for me to take all the pictures!
This was such a great family activity, sitting around the table together, the kids building their own creations with very little help from me. They were kind and happy and involved for more than an hour straight!