I couldn't find any info on how to thin it. But they say it's safe for kids furniture and toys, and if it cleans up with water then it must be an acrylic. Test a small amount with water to see what it does. Acetone and lacquer thinner also works with water soluble paints.
There are acrylic enamels, as well as acrylic lacquers. Like I say, just test a small amount with different thinners to see what works. Let it dry, give it a day or two and see how it holds up.