The Collaborative International Dictionary of English v.0.48:

oversimplify \oversimplify\ v. t.
   to simplify excessively so as to distort or misrepresent; --
   of facts, assertions, or communications; as, Don't
   oversimplify the rules.

   Syn: make too simple.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

oversimplify
    v 1: simplify to an excessive degree; "Don't oversimplify the
         problem"
    2: make too simple; "Don't oversimplify the instructions"