Catechismal Erosion

I remember several years ago learning the Westminster Shorter Catechism with my family.  It was a good cycle of family devotions; possibly the strongest we ever had.  My worry about teaching catechisms from birth comes from my few encounters with Latter Day Saints, who almost always subscribe to a faith that they can define, but do not understand.  They have memorized their confessions of faith.  How should Protestant catechism learning be different?  How do you teach truth without compromising the ability to reason?