I started giving Y&K crayons and pencils to color when they turned 14 months old. I let them scribble on blank paper for a start, then I started printing coloring pages from First School based on the theme or letter we are doing for the week for them to color. They progressed from banging the crayons/pencils to drawing circles but I didn't think they quite get what they are supposed to color and it didn't matter to me. I then bought a coloring book from the Popular Bookstore for S$3.60.
The pages had colored background and thick outline of the item with a sample colored item on top so older kids could follow the colors. I use this for my Chinese sessions. I will run through the name of the item in Chinese and the colors used in the picture but they are free to use any colors they desire. I actually regretted getting this coloring book as I later decided it's more economical to print my own. Also, I need to buy 2 books so both of them get the same coloring sheet to prevent any unnecessary fights. But when I see K recognizing the area he should be coloring, I thought the money was well spent! He was coloring with a purpose to fill the White area and I didn't expect that from him. So, a trick to let young toddlers understand the concept of coloring, use colored background so they could fill up the White space and do some real coloring.