I've also never had to get a puppy interested in toys (only experience is with terriers that loved toys from the get go), how do I go about doing that?
I highly recommend Kong toys. Stuff them with some kibble, maybe a treat too (making sure to detract from their daily ration), and their interest will be pretty strong, believe me! This has the bonus of stimulating your dog (always helpful with an intelligent breed like Shelties) and giving them the satisfaction of "earning" some of their daily food. It's good for your dog not to have everything (literally) given on a plate. You can stuff them creatively so that they're able to get some of the food quickly but getting all of it takes them a bit longer.