The paint isn't anything fancy: it's tempera in cake form. The advantages over other paints for kids are endless. really. It had bright and opaque, smooth colors, it mixes without being grainy, it can be used similarly to watercolor to make value and intensity variations, it's in a hard cake which takes FOREVER to use up (even w/ 150 students using 12 palettes all year, I only bought new paint every other year) , it doesn't crack or become powdery or chalky when dry, it cleans up well enough off of most surfaces (you CAN buy this in washable paint, but the colors are lame...just put a smock on your kid). Liquid paints DO have opaque colors, but they tend to become chalky when dry, and they crack and flake.
For teaching color theory, I recommend buying a set of only primary and secondary colors, then using the mixed complements and adding water for making neutrals and value changes. Black, brown and white are unnecessary, and disallows certain color theory lessons to be learned. So, buy 6 cakes and a palette to hold them. Young children (and I) prefer a brush with stiffer bristles...either a flat brush or round brush, with coarse bristles no longer than 1.5 inches, and about a half inch wide or smaller. You can get inexpensive sets at Michael's, Hobby Lobby, or JoAnns, or some like these (also inexpensive)
To use this paint, this is what I always teach kids: drop 3 brush-fulls of water on the cake, then stir until you see air bubbles form. By the time the bubbles show up, enough pigment has saturated the water to make a nice color. I like to start off by wetting and mixing all the colors I need before starting to paint. Use a flat plastic palette for transferring colors to be mixed (tertiary, neutrals, tints and hues, etc)
There are a couple of places to get these. I have the Richeson brand, from eNasco, but the Dick Blick always has quality products. These are kind of heavy, so I would check the shipping costs before buying them. I want to buy a new set for William (he's using mine right now) and Aldous, each, so if you want to do a bit of a coop with me (and you live near me), let me know.
For comparison, we have some watercolors made by Melissa and Doug. I usually like this brand, but they fell miserably short of producing a quality product here. It has a lovely big palette, a decent brush, and huge cakes of paint,but their colors are absolutely awful. They're translucent and have SO little pigment. Plus, they're missing some colors but have TWO greens and a black. Who's logic is this? Prang watercolors are always good, but the compartments are very small for young children and beginning painters. You can get sets you can refill tho, so that's always nice (from dick blick or nasco)
below I compared the opacity and pigment saturation of the M&D to the tempera cakes. The first color shown M&D, second tempera. Red, orange, violet and blue. On the bottom are mixed red-orange and blue-violet in the tempera. I prepared the paint the same way for this: three brush-fulls of water, stirring until air bubbles appear.
And, the final version of William's rainbow.
Thus concludes my kid paint review. :)