Ok, so I know I said I did not want to know, but eventually I got curious enough to do some digging. The elusive singer of “Purple Monkey In a Bubblegum Tree” was not easy to track down, and on my journey through Google, I found many other parents who were also in search of her. At first, I stumbled across this link, and erroneously concluded that the Kurtz-like figure in question was, in fact, Shakira. That would have been an extremely unexpected reveal, but not much more unexpected than the fact that Fisher-Price had partnered with Shakira for a toy collaboration at all. Which they did do! Apparently.
But no, Shakira did not lend her famous warble to the kick-and-play baby piano. That singer is one Deb Lyons, who is, it would appear from her Wikipedia page, a legit Broadway performer. I think we can safely conclude that the Fisher-Price gig was not a career highlight for Lyons, but rather an amusing footnote. I am still curious about the payment structure for children’s toy vocalist, and have emailed Lyons to inquire. I will update you all if I get an answer.
Related, here is an interview with another Fisher-Price recording artist, Kate Higgins. Higgins is not responsible for Edith’s specific piano (she did a different line of toys), but I found the interview enlightening all the same.