Purim is paradise [pardes and the English paradise are Persian words] for sex abusers. They themselves may be less inhibited while under the influence. Giving alcohol to younger boys can make them less resistant to influence and to abuse. Afterwards, the offender can claim it was silliness, not as claimed, abuse. I have heard too many stories of abuse that happened on Purim, typically involving older boys or young men with teens. Similar stories also happen other times of the year in Chabad with its ubiquitous vodka. That elixir of kiruv (outreach) knocks down boundaries and restraints.
Parents need to monitor settings where kids are, or be sure some other responsible adult is monitoring. They also need to regulate alcohol use. I am not puritanical about alcohol for under-age kids on Purim. But it becomes dangerous beyond limited quantities.
Alcohol kills in large enough quantities. Hatzolah organizations around the country report deaths and serious emergencies after Purim. Don’t let it happen to your kid.
Be funny, be smart, be happy afterwards.
Chag sameach! Happy Purim