My husband accidentally swallowed a tiny amount of radiator fluid when he was flushing out the car what should we do?

Should be okay: Phone your poison control center with the name of the fluid and do what they say. Ethylene glycol / antifreeze is toxic but a few drops will not hurt you.

Metabolic Acidosis: "tiny" amount is unlikely to cause symptoms, especially if liver and kidney function are normal. Do not wait for symptoms as may not appear for a few hours after ingestion ethylene glycol toxicity can be lethal and treatable if addressed medically in a timely fashion. Your er doctor will obtain urine and blood tests to determine if treatment is needed and may be able to determine if accidental.