Hello! Thank you for the query. Windshield washer fluid could cause stomach irritation. Many ingredients of washer fluids could burn the surface of the stomach. This could result with some kind of a wound of the stomach called an ulcer. Stomach or esophagus inflammation is also possible. He may suffer from upper middle abdominal pain which can appear after a meal. I suggest you to try mild diet for few days and see if the situation will improve. If not, stomach tests like gastroscopy might be necessary. Abdominal ultrasound, liver tests, amylase, urine analysis should be also checked. You should visit podiatrist for proper diagnostics and treatment. In a meanwhile please keep your son well hydrated. Low urine level, dark urine and weakness indicate renal failure. In case of such symptoms, ER should be visited. Hope this will help. Regards.