Most toy designers have a minimum of a bachelor's degree in some field related to art or design. Coursework can include model making, two- and three-dimensional visualization, concept problem solving, and even child psychology.
Many toy designers also need to understand the fundamentals of production and business, so courses or degrees in business practices or marketing might also prove useful. You want to sound professional when you're at pitch meetings for your toy creations.
As in any creative industry, experience counts a great deal. Those wishing to score jobs in the toy design field should have, in addition to their education, a portfolio of work to show prospective employers. Having an actual product on the toy store shelves couldn't hurt, either.