Welcome to planDisney, Janet. Thank you for bringing your question to us.
At this time, theme park attendance is being managed with the
Disney Park Pass system. All Guests ages 3 and up require a Disney Park Pass reservation in addition to valid
admission in order to enter a theme park. Disney Park Pass reservations are not like dining reservations, where everyone in the party needs to be on the same reservation to be seated together. As long as everyone in your party has a reservation for the same theme park on the same day, you'll be able to enter the park together -- it is not necessary for everyone to be on the same group reservation.
Currently, it is not possible to add a Guest to your previously booked Disney Park Pass reservation. The extra Guest would need to make their own separate Disney Park Pass reservation. That being said, I just took a look at the
theme park reservation availability calendar, and I see that at the moment,
Magic Kingdom Park is unavailable for June 21. I encourage you to check back frequently; other Guests' plans may change and there is the possibility that a reservation might become available. My other suggestion for your extra Guest would be to add the
Park Hopper Option to their ticket and make their Disney Park Pass reservation for a different theme park with availability that day, and then join you at Magic Kingdom Park after 2:00 pm when park hopping hours begin (subject to availability).
Janet, I hope you are able to secure the Disney Park Pass reservation you are looking for. If you have any additional questions, please stop by planDisney again anytime.
Anne Marie