If I was going for one day with little ones, this is the plan I would follow:
1. Consider purchasing ridemax (ridemax.com) It is 16 dollars or so, but lets you figure out the best plan of attack to minimize line waiting. For what you will spend on this trip, it is a small price, IMHO.
2. Since your kids are so little, you will probably spend a lot of time in Fantasyland. Fantasyland has no Fastpass attractions, so you need to do the following things:
Be in line half an hour before the gates open, tickets in hand (prepurchase through Disneyland.com, or at a
Disney store)
Go on a Wednesday, if you can. There is early entry for FL attractions on M,T, TH, and Sat, and Friday/Sunday will be busy. On EE days, (which you will not be eligible for with a one day ticket) FL will be FULL by the time you can get in.
3. Go to Disneyland.com, and check out the show times. Use the shows (Snow White, Billy Hill) to give your family a break in the afternoon.
4. You might want to schedule an early dinner/late lunch at DL hotel/Goofy's Kitchen, to give your family a break. YOu can take the monorail.
Have fun!