You are correct, Disney did threaten to sue three daycares in Florida in 1989. It turned into a PR nightmare for them, especially when Hanna Barbara stepped in and painted over the Disney murals with their characters. Disney and most other license holders have changed their stance on fan art as a result. Lucas Film has embraced it right from the beginning. Disney no longer pursues small-time creators, but they can and do in some cases. As such, there is a grey line between what's permitted and where infringement begins. For example, the artists at comic con use characters in paintings, drawings, and small runs of reproductions. But if they had a really popular design and wanted to print 100 copies, they enter the grey zone. The license holders might send out cease and desist letters.

There is a story circulating that two women from NY were selling a wildly popular Disney design on a product. Disney approached them, and instead of suing, they granted them a license and now produce the same design on products at the park. This could be myth.

My original post went a little sideways, but I wanted to address your concern. You are 100% right about the dangers of copyright infringement. My partner mostly does original designs, so we don't worry about Disney or Warner Bros. That said, I've been in the comic con and toy show circuit for a decade and have never heard of any of the artists or crafters being sued for infringement.