stomachache vs tummyache

stomachache

noun
  • A pain in the abdomen, often caused by indigestion. (The pain is usually lower than the stomach and related to the intestines.) 

tummyache

noun
  • Any pain in the stomach or abdomen. 

How often have the words stomachache and tummyache occurred in a corpus of books? (source: Google Ngram Viewer )