Babyganics Scrub-a-tub is what I use now, used to love scrubbing bubbles but became allergic to the chemicals in it. Babyganics is all-natural, simple ingredients and a few sprays takes everything off with a soft reusable rag, not much scrubbing needed at all. It doesn't get simpler or cheaper than that. I can find the bottles for a few dollars at Target, amazon, or babyganics.com and they last forever.

Crayon is just wax and coloring, so I find the easiest way to get it off a hard surface is a dry soft cloth-an old towel is perfect b/c the loops in the fabric get it off easy with no force needed. If the crayon is on a soft surface like fabric, I've heard the best way is use an iron or steamer to heat it slightly and then press an absorbent fabric or paper on it to soak it up, but it didn't work well for me on my car seats.

Both the paint and the bath chair have that 'pebbled' surface, which is why we're having so many problems.