I know you can see what books your pet has read or foods it has eaten, but is there a way to see what toys it has played with?

As far as I'm aware, there is not.

I also tested to see if I'd get the notice "this pet has already played with this item" and it did not happen. Played twice with the same pet and the same toy, giving time for the cache to update between plays and nothing changed.

There was some talk several years ago about making a "toy achievement" like the "gourmand" achievement. Staff took some steps to make it happen (changed all the plushies from toys into just plushies and did some clean up of the toy items), but never completed the process. If that's still on the back burner, and they ever get around to actually doing this achievement, then there will likely be some tracking of toys played with, but I'm not holding my breath.

Thank you so much for the info! I wasn't sure if there was something I was missing! I really appreciate it!