We usually steer clear of Fantasyland in the morning as we don't have any kids. But when we went with our nephew/niece, it was VERY busy (and it was the off-season). If you go there first, I would suggest going straight to Dumbo, then Peter Pan.
What we like to do first thing on busy days is walk through Adventureland and pick up a FP to Indiana Jones. Then we continue straight and head to Splash Mountain. Depending on what time your FP is for, you could also hit Big Thunder, Haunted Mansion and Pirates before returning to Indiana Jones to use your fast pass. Then eat some breakfast!!
When its busy, I like to make use of one area of the park. Get some of your "must do" rides over in the a.m. (you can always re-ride them later) using fast pass. I like our above method because there are so many big rides in that area (Adventureland/New Orleans Square/Critter Country)