When I was at the Maui Marriott this last summer the kids club loaned out kid stuff like boogie boards, sand toys, ect for free just check it out from them and bring it back at the end of your stay or whatever day you are done using it.
We also stayed at the Hilton in Oahu that same summer and they did not provide any such "free" loaner items.

Just tried you sell you the sand toys for $20 pool side! Well, I asked at the bell hop desk if anyone had left any kids sand toys that we could just borrow and bring back...........they went and checked some room and brought us back a whole bag of them and told me I could keep them!

Of course I had no desire to keep them, so I returned them along with the suggestion that they offer such a program in the future.
It is like the take a book, leave a book librarys, why not do this with kid toys???
I would just ask around to various workers at the resort, chances are someone left just that and you are free to use it. FYI.......my husband travels a lot for work and he says this is true with cell phone chargers too! He asked once when he frogot his and they produced an entire box of them and he went thru it until he found one that fit his phone. They told him to keep it if he wanted b/c people froget them at the hotel all the time! Good to know these things are getting second homes and not ending up in a land fill somewhere.