Don't limit what they can offer due to the fact that they don't have many supplies to work with. You can even consider offering them craft supplies such as glue and glitter, cotton, ribbon, and other items that can all become a part of the Spongebob coloring pages they are completing.
Very young children don't know the places where they are not allowed to draw and might do their coloring on the floor, walls, furniture and so on; apart from that they like tasting everything they hold in their hands like crayons, markers or paints. That's why they require continues supervision. But older children can work independently, giving you lots of free time, although they also enjoy a parent coloring along side them. Every child also likes to be appreciated by his parents. In this case we recommend to post children's best creative masterpieces in a prominent place in the house. It will give more confidence to your kids.
The online coloring stuff with printable option might be the best of its kind as the child does not have to finish his coloring in one go, he can wait and try his hand whenever he wants to. Or he can get the prints once he is done with the artwork online. What pleases you more? The child who is happy and busy or the one who is always complaining of not getting the stuff he wants to color. Of course the latter option can be the choice.