In line at the craft store the other day Luke picked up a magazine that had a picture similar to this in it and started immediately begging to do this. I wasn't sure exactly what the material inside was; I thought it might be cornmeal. I started googling around and found this which is actually something called cloud dough (flour + baby oil) and is slightly moldable. One trip to the dollar store later and we have a bucket of cloud dough out on the back patio.
Our bucket isn't quite as long as the one in the picture, but that just makes it easier to store. It gives him some depth to work with so that he can dig holes and build piles and such. It is messy! You ARE in fact, giving your child a bucket of flour to play with, after all. I would definitely recommend it is an outside activity.
Luke was so excited. I only had three vehicles in it when I showed it to him and he immediately ran to his room to get some more trucks.
Total cost: $2
Total time: 3 minutes to mash together. Hours of entertainment
Final verdict: I don't think I could tear him away from it if I tried. He's going to need a bath tonight, but at least with the baby oil it has a nice scent to it. Maybe it is softening his skin too?