Indiana law makes it a misdemeanor offense for an individual (regardless of age) to knowingly or intentionally visit a location where alcoholic beverages are being sold to minors.  This would include a location that merely charges an entrance fee or “cover” and then provides alcoholic beverages to minors inside. If your son were merely present at a location where minors were consuming alcohol (but not paying to attend the event) and he himself was not consuming alcohol, he would not likely face any charges.
Under Indiana law, no one under the age of 21 can possess, consume or transport an alcoholic beverage.  The law does make some provisions to allow an individual over the age of 19 to sell alcoholic beverages at a licensed premises.  Additionally, Indiana law grants limited immunity to minors who call 911 to report an alcohol related health emergency.
Any venue (be it a nightclub or a friend’s basement) that permits a teenager to drink is not acting in the best interest of the teen.  Study upon study has demonstrated a correlation between underage drinking and increased health risks.  Academic performance suffers and increased risk-taking (such as drunk driving, fighting, and sexual activity) often occurs.  Teenagers who abuse alcohol become young adults who abuse alcohol.