The bad news is that for the child who does get a burn from swallowing a strong cleaner, the problem often doesn't stop with the pain of the burn. Scarring follows that initial injury and strictures form. There may be a week or more after the caustic stuff is swallowed before more signs of trouble arise. In some cases the esophagus will never be normal again and major surgery to replace it is needed. Always keep chemicals and cleaners in childproof containers - never pour part in jars or other storage containers.
Prevention really is better than cure.