I'll be going in August with two kids (4 and 6). We've been going yearly for the past four years, the first visit with the older one being 2 and the younger one merely being 10 months old. Key for us is preparation. For this trip, I've looked at the height requirements for each ride (
http://disneyland.disney.go.com/plan/guest-services/height-requirements/) to make sure I can prevent last moment disappointment when big sis gets to ride something and little sis doesn't.
Both my kids love the Redwood Creek Challenge trail. The zip-line and the rock climbing activity are for kids 42" and above only, but all the other climbing, sliding, etc. is open to kids of any age.
The indoor ride both kids enjoyed was Winnie-the-Poo. As all indoor rides, it can get a bit loud, though, so if your little one has sensitive hearing, you might consider bringing earplugs (or, in a pinch, crumpled up pieces of tissue work, too).
Also, you can find "point-of-view" videos on You Tube for any ride imaginable. Just search for "
disneyland" or "california adventure" and the name of the ride. This way your kids can see what the ride will be like and have input into my planning it into the trip or foregoing it.
Enjoy! Though it'll get exhausting, it's so much fun watching kids that age take it all in and being completely carried away by the magic of it, not all cynical and so over it all as they might turn once they become teenager...