1.  n. the penis. (Usually objectionable.)  Put your doodle away, Jimmy, and flush the toilet.  
2.  n. feces, especially a baby’s feces. (Baby talk.)  Billy’s got doodle in his diapers.  
3.  in. to defecate.   (see also doo-doo. Baby talk.) The dog doodled on the back porch.