bostonmama

Yep, if/when changes are made, that's about all you can do.  
I hope you get what you want!

Yes, I understand, thus my original post asking if spots become available.  Probably doesnt matter to you but for others potentially in this situation, when I just logged onto the Cruise planner it showed "2 spots available" but I couldn't select them (someone else must have had them in their cart) so clearly spots become available.  A couple minutes later it shows "sold out."  I'll keep checking.  I'm happy with our low fare for balcony stateroom and I know we'll enjoy our time whether we get into the water park or not. 

Thanks!!!  Enjoy your trip with your son!!! 🥰

I’ll keep my fingers crossed for you, too! I’m doing a mother-son trip the same week, but the thrill park is not sold out yet on the 19th. I was checking the cruise planner pretty frequently for a while, and I noticed that the beach club would vary from being sold out sometimes to having a few passes available, as people canceled, I assume. So I think there’s hope if you check back often. 🍀🍀

No I don't think there is a way to see Cruise Planner availability until after you have booked.  However, you could find a roll call group (on this site or elsewhere) or a Facebook group for the specific cruise.  Then, ask the people who have already booked the cruise what they see.
For @bostonmama's situation, I think this was a risk of booking a cruise that is only weeks away.  The first people probably booked it almost 2 years ago at this point.  Cruise planner purchases are shut off about 3 days before the cruise in order to transfer everything to the ship's records.  Some people may rearrange their plans right before that so I would keep checking multiple times a day to see if availability has changed.  Once on board, you can only cancel for a refund up to 24 or 48 hours before an excursion (I forget which) so some people may wait until then to change their minds.  It's not hopeless, but I have no idea what your chances are of getting tickets.  As others said though, if it's sold out the lines will be long so go ashore right away!

If they are indeed sold out, the lines will be long.  My kids have complained about the long lines in the water park even when it wasn't sold out.  
If you do manage to get passes for it, my advice is go as soon as it opens, as it will only get busier.  And go on the bigger slides first.  Save the wave pool for the middle of the afternoon when the lines for the slides are longest.  

This raises a question in my mind:
So, is there a way to see if a package like the waterpark is sold out before you purchase a cruise or put a deposit down on a cruise, a package that you are purchasing for the almost sole reason of taking your kid(s)/grandkid(s) to?  Seems only fair to me, especially if you purchase a Non-Refundable Ticket.  
I honestly don't know the answer to this question.  I'm assuming you can't see the "cruise planner" until after you put a deposit down or purchase.  

I'd keep checking the cruise planner website at least daily till it closes out for your cruise as well in case more open up. 
From looking at the Cruise Time Tables website, it looks like you'll be sharing the island that day with Independence of the Seas. Hopefully you have some luck since you're not sharing the island with another larger ship like another Quantum Class or Oasis Class ship. 
It is possible they will be entirely sold out though, and its a bummer that Anthem doesn't have any on board water slides either.