Hey there, Amy!
Welcome to planDisney! I know that traveling with small kids involves a lot of gear already, so I don't blame you for wanting to leave the car seats behind. I found some ways to work with transportation flying into California when my kids were small, I'd be happy to share a few ideas with you.
There are a couple of options for
getting from the airport to the Disneyland Resort. In your case, I would recommend reserving a private car service. If you do a web search along the lines of "car service from airport to Disneyland Resort with car seats for children" you should be able to find a few that allow you to rent car seats when you make your reservation. I used a variety of providers over the years, always checking out their reviews online, and never had an issue. I'm sure you'll be able to find a great provider, there's plenty of them out there!
Another option for older kids might be portable boosters. I had some for my kids that would fold up to fit inside their backpacks for traveling. They were also really handy to have when getting rides with friends or family at home!
The good news is that once you reach
Disney's Grand Californian Hotel and Spa your transportation becomes a breeze! You'll be able to
walk directly into Disney California Adventure Park from the hotel (SO nice!) and Disneyland Park is also a short walk or Monorail ride away. It looks like you're traveling in May, which is one of my favorite times of year to enjoy the resort. Usually the weather that time of year is completely beautiful, so plan to spend some time at the beautiful
hotel pools!
Amy, I'm confident that you'll be able to work your magic and find ground transportation that you feel good about.
If you have other planning questions I would love to help you! Keep moving forward!
Amanda