Disney Land

Disneyland is not as spread out or broken up as Disney World is.
Disneyland has 2 parks, Disneyland and California Adventure. They are directly across from each other with an open area between. On super busy days the lines for both parks to get in can sort of merge together to give you an idea of how not huge it is. Both parks share the same ticket booths and security checkpoints. Parking is in the same locations for both parks.
Disneyland is set up into lands just like Disney World is. So Main Street USA, Fantasyland, Fronteirland, Adventureland, Tomorrowland, Critter Corner, New Orleans Square, Toon Town. None of these are super huge by any stretch. You get to each land in a few moments of walking.
You need separate tickets for Disneyland and California Adventure. You can get park hoppers so you can go between both parks in the same day. Each park is within walking distance. We have annual passes and have for years now. We will very often spend part of the day in Disneyland, walk across to CA Adventure for dinner and catch a ride or 2 then go back over to Disneyland to close out the night. It's extremely easy to do. Downtown Disney is also directly attached and easy walking distance to everything. The tram from the parking structure actually drops you off at Downtown Disney.

The Disneyland website has some very good maps on their website to give you a better idea of how everything is spaced out. Also, if you have a smart phone (iPhone or Android) I highly recommend the free app called "Mousewait". It is an invaluable resource to have in the parks. It has crowd sourced wait times for everything in the parks as well as a fantastic lounge with extremely helpful people as well as real time updates from people that are in the parks. There are also some great resources built into the app with a lot of information to help with your visit. I love it and use it all time when we're at the parks and enjoy the lounge when I can't be there to see all the live pictures and find out what's happening in the parks.

Depending on the age of your child, I would choose Disneyland for the younger set. There are more characters walking around to see, fewer height requirements on the rides and you will get a more traditional Disney experience. There are also more rides, the park is bigger and there is more variety.

CA Adventure is the newer adjacent park. It has great rides but I say it's geared for the older kids who want more of an thrill than an "experience" if that makes sense.

Something I learned is you can now bring food into the parks, just no glass bottles. Food has always been incredibly expensive inside the parks so being able to make PB &J sandwiches in the hotel room or pick up Subway sandwiches on the outside and carry them in your backpack will save you a bunch. Bring water bottles too.

Have a great vacation!

As others said, there are two main parks - Disneyland and CA Adventure. By far Disneyland is the place to go if you only have time to visit one park. Kids of all ages will have fun there and it is a lot more fun. Plan to spend a full day (though, if the kids are really little, you may want to plan a mid-day break/nap) and the whole family will have a really great experience.

The biggest thing to remember is don't try to do it all. Don't feel like you have to rush from ride to ride or stress out if lines are too long. Don't worry about crowds or if the kids would rather go meet the characters than ride the rides. The day will be the most special if you just enjoy the time you have and the things you are able to do, rather than worry about the things you don't have time for.

We did both in one day when DS was 4. Soaring Over California is one attraction absolutely not to miss. It is at California Adventure. The two are right across the parking lot from each other.

http://www.isitpacked.com/disneyland-crowd-forecast-predi...

A day is plenty of time to visit. DL has more to see/do than CA Adventure. I like CA, but DL is just "better."

I'd avoid Universal Studios. I can't stand that place. Even my kids (14 & 9) don't care for it.

I agree to choose Disneyland over California Adventure.

Disneyland hands down.

You should go on line and do some research and map it out since you only have one day. Even only doing Disneyland in one day can be exhausting. They both have great things to offer and if possible you should extend your stay to 2 days if you consider doing both. Disneyland is not to be missed, especially if you have never been.
However California has an awesome new area for Cars and they have a Bugs Life for little ones and Toy story. Their parades have the more current characters as well. World of Color is spectacular and you have never been on a ride like Soaring! Also in the arcade area there are rides for youngsters including a very jerky rollercoaster.
But if it is only one day then I would stick to Disneyland...they have Princesses, need I say more!