Drugs & Alcohol - My son/daughter is under 21 yrs old, he/she is at a house party where alcohol is being served, can he/she be arrested?

Yes, anyone under the age of 21 found at a house party is subject to arrest whether or not they have been drinking. The same goes for in a car. If there is alcohol in a car, and they are not with their parents or legal guardian, the law states "Whoever, being under twenty-one years of age and not accompanied by a parent or legal guardian, knowingly possesses, transports or carries on his person any alcohol or alcoholic beverages.."