Swallowing a small amount of mouthwash is often harmless and rarely causes anything other than mild and temporary upset stomach, although the mouthwash you swallowed might also cause some mild diarrhea or nausea.
The mouthwash can contain ingredients that can irritate your digestive tract if ingested, but small amounts of mouthwash is nothing to worry about.
After you do swallow a small amount of mouthwash, you may feel a bit queasy, although the symptoms will often go away within a few hours.
If you do swallow a small amount of mouthwash, you should drink a small amount of water to dilute the mouthwash in your stomach, but don't induce any vomiting.
However if you swallow a huge amount or if a child swallows any amount, you should contact a doctor or the poison control center at 1-800-222-122.
Although even my kids have swallowed small amounts of mouthwash and have been fine, but look out for any signs of illness and take them to the doctor if needed or the ER if it gets serious enough.