Hello there Alice,
Welcome to planDisney and thank you for your question! I'm so glad to hear that you'll be making the trek to sunny California for a visit to the Disneyland Resort. You're going to have such a great time!
I'm a huge proponent of the
Park Hopper option and almost always add it on when I visit the Happiest Place on Earth. It allows for a lot more flexibility during your trip so you can hop back and forth between parks starting at 11:00 AM each day and as park capacity allows.
To get this added to your existing tickets, you'll want to
contact a Cast Member at the Tickets line. They'll be able to see the specific details of your situation and let you know if your tickets are eligible for this option. In case you're having trouble accessing the links, their direct phone number is +1 (714) 781-4636.
Additionally, it looks like you'll be visiting during the
Halloween season, so make sure to keep an eye on the
Disney Parks Blog to see all the fun things that will be happening around the Disneyland Resort during your visit!
Thanks again for your question, Alice! I hope you have a wonderful trip to the Happiest Place on Earth later this year.
Have a Magical Day,
Greg