Many crayon artists (you can find a few online) use solvents to soften their appearance. It can be a wonderful look but, personally, I love the pixilated look the crayon creates when applied just as is. Look at the art examples in this post _ you can see the speckled look crayon has when applied in layers. This adds to the realism, especially when creating an out_of_focus background, such as in these two images.
There's also a kind of colored pencils that's called water_coloured pencils. The way of application is just the same as colored pencils. However, with this media you can achieve a watercolor effect by dipping a brush in water and brushing along the colored areas with it. It's actually a fun media to try especially if you want to use a watercolor but find the mixing with water hard. It's easy to use as well.