A good solution may be water coloring - booklets with cards, on which are placed a small amount of paint in the form of dots. Just move the brush soaked in water to give the pictures color.
Water coloring is an interesting and brilliant option in its simplicity, but it has a disadvantage. The water-based painting with a creative toddler becomes one-time use (usually only contains a few pages), and then you can only throw it away.
Recently, I came across the Colorino booklet from the Creative series "Underwater Adventure", which is also a water coloring, but unlike any other. The set contains a booklet with 4 pictures and a pen that needs to be filled with water. If you want to paint a picture, just use the attached pen filled with water. This is a very practical form of painting with water because, above all, it does not require the use of a brush and water, which often spills with a clumsy toddler.
An additional advantage of the booklet are extremely intense and vivid colors, which cannot be achieved with traditional watercolors, we usually have pale, faded colors. But this is not the end of the book's advantages - another option is to use it many times. After drying, the water evaporates and the picture loses its colors so that the booklet can be used again (!).
The price is slightly higher than standard watercolors (around PLN 20), but the expense pays off quickly.