I am not a Disneyland expert but here were a few tips and tricks that I'd love to pass along from a 1st timer's point-of-view.
1. Stay at a Disneyland hotel if at all possible.
We stayed at the Disney Grand Californian and it was wonderful. A quick walk to Disneyland (it's on Downtown Disney) and connecting to Disney CA Adventure Park it's a perfect location. The actual hotel is lovely and the rooms nicely appointed (small but with bunk beds!) but the draw is the location. You can easily walk to and from the park. Key when you have small children that very quickly need a nap!
You also get to go into the park one hour early (they trade off between CA Adventure and Disneyland though, so check ahead). This is a nice perk if you're ready to start your day a little ahead of the regular throngs of people.
2. Pack ahead, bring your own treats and snacks.
This tip was passed on to me from my experienced friends. I bought small snacks in all shapes and sizes ahead. Snacks like Annie's bunnies, gummies, granola bars, fruit tape, juice boxes, etc. These were easy to pack and keep. I also recommend bringing cut fruit, cheese, pb&j sandwiches and meat chunks. You know, real food! This will cut down on the amount of stops that you need to make at "real = expensive" on site restaurants.
Same goes with treats. At the park the options of mickey paraphernalia are endless. Your children will be tempted by balloons, lolly's, clothing, dolls, wands, dress up outfits, jewelry, big spinning mickey faces...you get the idea. Shop ahead at your local Disney store, Walmart, Target (dollar area!!) or Dollar Store. Bring your own Disney treats and clothes!
3. Glow sticks for the parade.
If you and your children are able to stay up until the closing parade and firework show I highly recommend going. It was my favorite part of Disneyland! Seeing Tinkerbell fly above the castle (how do they do that?) and all beautiful fireworks reflected in my children's little happy faces was a moment I'll never forget. I was also happy to have brought our own glow sticks/flashing glow spinning wand thing so that I didn't feel pressured to pay $12-15 for the Disney ones! I bought mine ahead at the Dollar spot at Target for between $1-$3 a pieces. Score!
This one is mandatory for the younger crowd. Plan a nap in your day. Trust me. I understand the push to go-go-go when you've spent a million dollars on tickets and there are SO many things to see. But worn out, tired, crying children is NO fun. Take a nap and come back refreshed.
5. Ask for photos.
We received a free signed photo of Anna and Elsa when we checked in at the hotel. We later received free signed photos of Mickey and Minnie from the Disney store when purchasing their Minnie ears (one item not to buy ahead). Disney has tons of autographed photos, just ask!
Try to wait if you can to purchase your morning coffee inside Disneyland as they have a huge Starbucks right on main street. The Starbucks cups have cute little mickey ears on them, while the Starbucks outside the park does not.
7. Adjust your expectations.
If you are a first timer to Disney, or perhaps you have been but never with children then you may need to set realistic expectations. With small children you won't be able to see as much as you would think. Between bathroom breaks, diaper changes, snacks, mini-meltdowns and a million questions it can be slow going.
You could make a plan of all the rides you'd like to take, but I'd suggest keeping it to a very very loose plan. Your kids may not even care about most of the rides.
I found that my kid's favorite experiences were meeting characters. They were over-the-moon to meet Minnie, Tinkerbell, Aurora, Mickey, etc. We prioritized time to wait at the Princess Castle to meet them as a result. We took a million photos (don't worry, Disney has "professional" photographers at each photo op if you don't have a camera) and the girls love seeing them now that a few months have passed since our trip.
My day consisted of the Flying Dumbo ride, meeting characters, It's a Small World and a few other small rides and that was just fine. My girls had a great time and those smiles say it all!
Good luck and have a great trip!!