I think that's a great idea. When my H D, and SS was little, they did this. H got some big canvases and some bright paints. He would dip SS's feet into the paints and he would swoosh them around on the canvas in different colours, same with the hands. Ended up with bold splashes of colour and the odd discernable hand & foot print - lovely.

Charity shops often have cheap printed canvases too, or maybe a nice board with some printed pics of the kids that you can add new photos too - or a board that has some of their art pinned onto it?

T 13 M 7
Me 48 H 46
SS 15
BD 7.14 PA
D final 5.16 (H filed)

We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus