Hello there, Madalyn!
Thanks for stopping by the Disney Parks Moms Panel with your question. It sounds like you are getting ready for a vacation to remember this December! We took my son on quite a few Disneyland Resort vacations as an infant and toddler, so I know the little ones in your group will have an amazing time like him.
When it comes to attractions, infants and toddlers can ride any attraction that does
not have a height requirement. You will find when you search online or within the Disneyland app that there are actually so many of these attractions that you can all experience together. My son always loved classics like "it's a small world," Peter Pan's Flight, Dumbo the Flying Elephant, and Mad Tea Party to name just a few. You will find that these attractions are more plentiful in Disneyland Park but still there are some great attractions for the whole family in Disney California Adventure Park as well. My son always enjoys The Little Mermaid ~ Ariel's Undersea Adventure, Monsters, Inc. Mike & Sulley to the Rescue!, and Pixar Pal-A-Round in Disney California Adventure Park, for example.
With so many little ones you will definitely want to take advantage of the convenient
Baby Care Centers located in each park. These offer private spaces to feed and change your little ones away from the hustle and bustle. I also recommend bringing or renting a stroller and making sure it is easy to identify in a crowd. This will come in handy when you are searching for your stroller after exiting an attraction.
I hope this helps, and please feel free to return with any other questions as you plan your magical vacation!
-Jennifer