Hello Adrianne and welcome to 
planDisney!
Thank you so much for taking the time to visit us today, I’ll be more than happy to help. A very happy belated birthday to your little Mouseketeer. I was in the same boat as you with my little one, except with Walt Disney World Resort tickets, a few months ago as well.  
What you will want to do, Adrianne is 
purchase a theme park ticket for your son. I do recommend checking to see if there is still theme park reservation availability on the day you already have reserved for yourself, first. If there is, then go ahead and purchase and 
reserve the same day, with the new ticket, for him.  You will repeat the same steps you did with your tickets by first linking them to your 
Disney account. It’s totally fine if the reservations are made at separate times, all that matters is that the reservation date and theme park are the same. 
If there is no availability left on the date you already have reserved, I do recommend moving your existing reservations to a later available date. Again the 
theme park reservation availability calendar, will be your Mouseketool when it comes to reserving your theme park days.
Adrianne, I do hope this helps better prepare you for this 
exciting family adventure. Please be sure to let us know if there’s anything else we can help you with!
Have a Magical Day!
-Shantel