I’ve never done anything related to toys, but here at work we have three books which may be of interest to you. I haven’t gone through any of them extensively, but they are good references.
“Plastics Design Handbook” by Dominick Rosato, Rosato, & Rosato - very technical into almost every aspect of making things out of plastic, not just part design.
“Plastic Part Design for Injection Molding” by Robert A. Malloy - smaller and more to the point than above, but still a lot of detail (more than you’ll get in an ID education for sure) and covers a just about everything you need to know for injection molded plastic part design.
“The First Snap-Fit Handbook” by Bonenberger - A small book, but more than you thought there was to know about snap fits. “Plastic Part Design…” covers them as well, but this book goes really deep.
I hope that helps. Again, I haven’t combed any of the books extensively, but they’re good reference and my boss must’ve they were good when he bought them 
. I’m not sure how old they are, though I’m sure 98% of the content is still just as relevant.