Disneyland is not as hard to "plan" as Disney World because there are only 2 parks and downtown Disney. I would plan a full day for each park. Then, if you have a hopper pass, you can spend a portion of the day at both parks for any other days you plan to be there. Start in one area and move across the park. Don't go from one side to the other, that will take too much time away.
Go to Disneyland's web-site now...
...to see if there are any special events going on while you will be there. Plan your days accordingly.
...Check to see what, if any, rides are closed right now. That way you'll know not to even venture to them.
...Check height requirements for the rides. That way you will know in advance who is big enough for what ride. They offer a switch-out programs, where you don't have to stand in line separately to keep those who don't/can't ride a ride away. You all stand in line, then one parent goes and one stays with non-riders. As soon as that parent gets back, the other parent goes with the other one stays with the non-riders.
Unless you plan on going back to your hotel for all of your meals, you will need to plan at least one meal per day at the parks. You're looking at about $10 per adult meal and $6-7 for a child's meal. Advice there would be to eat a big breakfast, get a snack mid-day, then go back to the hotel for dinner. Honestly, I wouldn't make any grand plans for cooking too much. You are going to be just as exhausted as everyone else, then have to cook too!
Get a double stroller for the 6 and 4 year olds. They will get tired. Bad news about renting, you have to leave the stroller at the park. If you have a sleeping child, or one too tired to walk, you will have to carry them to your car. (and you're just as exhausted too, haha) I have hilarious pictures of my son and niece (5 and 4 at the time) splayed out in the stroller when we went to Disney World 2 years ago.
Go to Wal-Mart and buy lots of the cheap rain ponchos. You can find them in the camping section. They used to be 87 cents and were basically disposable. We always take at least 2 sets. I a set into my purse, then we have them if needed. If we use them, we trow them out then start with a new set the next day.