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Try one (or all) of these options that add texture to the painting process or change the quality of how the medium feels:
There's virtually no way to mess-proof your kid. I suggest dressing him in clothes that you don't really care about. Even though the red finger paint says that it's washable, if you happen to let it sit for a few days it's not as likely to come out. One time, during a preschool art class that I was teaching, I had a 4-year-old ask me if he could have rubber gloves so that his fingers wouldn't get messy while painting. Here's my answer: NO! This project is all about exploring the paint and getting messy in the process. If your child freaks out over the mess, try something that is more on the tame side such as the "clay paint" I describe in the previous post.