If you have to go during Spring Break season, it'll be much more crowded, so be sure to get to the park first thing when it opens.
A tip - look at the calendar on the Disneyland website, and try to go on a day when the hours are shorter. If the park is open until Midnight, that means Disney knows it will be a busy day!
Days when the park closes at 8 are PERFECT for taking a 2-year-old. The park won't be crowded, and a toddler's not going to stay up late anyway. The only disadvantage is that there may not be a parade.
As for visiting with a two-year-old, I find that a tough age for visiting a theme park. The child likely won't remember much more than a image or two - the event is more for the parent or adult in the group. It can be fun, but you have to visit with no expectations whatsoever. A child might hate all the top attractions, but be absolutely enthralled watching a custodial cast member sweep up a sidewalk with a pan and broom - for 20 minutes. (That pretty well describes one Disneyland visit with my then-two-year-old son.)
That said, I have to recommend the most unique Disneyland attraction for a two-year-old. Go into the baby care center at the end of Main Street (behind the Corn Dog Wagon) and ask to use the potties. Back by the changing tables are a few porcelain toilets - scaled down to toddler size. Unlike other theme park toilets, not only are they potty-sized, they don't have automatic flush, either, so no on gets scared on them. My kids *loved* these when they were potty-training.
Walt Disney World's Magic Kingdom
Disney's Animal Kingdom
Disney's Hollywood Studios
Disney California Adventure
Universal's Islands of Adventure
Universal Studios Florida
Universal Studios Hollywood