Is there any over-the-counter toothache pain reliever for my four year-old child?

Yes: Acetaminophen, ibuprofen, and a dentist, not necessarily in that order.

Pain and Kids: I would suggest some childrens Ibuprofen or tylenol (acetaminophen). Makes sure you read and follow the driections on the bottle. You could also consult your pediatrician. Any other over the counter product such as orajel will only provide very temporary relief. If the pain is really bad i would suggest seeing a pedodontist to help with the source of the pain.