I would think a standard breadboard would be a good way to teach kids circuits. They are easy to hook up and easy to change.
But if you want them to make more permanent circuits, you could print out some larger boards that have trace channels that are separated by wider walls so that it is easier to fill them without overflow and then no sanding would be necessary.
Like most water based paints, when put on thick, the Cupro-Cote paint dries on the outside first and leaves the inside gummy for many hours. You really do have to wait overnight for the components to be held fast.
Another possibility you could consider, would be to draw a schematic on a piece of paper or cardboard and have them fill in the lines with paint and and then glue in components where the symbols are. This paint is very conductive and even a thin flat painted line is very conductive. It does dry faster on paper 3d printing services baroda gujarat india
It also sticks well to almost anything. You could draw a schematic on a piece of Plexiglas and they could fill in the lines and make transparent circuits.