Warning: Soapbox ahead.
On Purim we celebrate the ultimate joy of a sudden national rescue, and our sages taught that we should imbibe alcohol at the Purim Seudah as part of this celebration. Just as we abstain from various foods and from drink at certain times of the year to induce sadness, so we indulge in various foods and in drink at other times of the year, to induce joy. The gemara’s standard for imbibing is to drink until we cannot tell the difference between “Cursed is Haman” and “Blessed is Mordechai” (Megilah 7b).
Authorities differ on how much to drink, but the following is clear: An adult who is medically, psychologically and emotionally able to drink, and who has a designated driver, should drink some amount of alcohol - preferably enough that he feels lightheaded (Shulchan Aruch, Orach Chaim 695:2). One should enjoy his Seudah, drink a little, and then sleep off the effects of the alcohol.
Many people, and I include myself in this number, have embraced the practice of drinking minimally at the Purim Seudah and then fulfilling the state of intoxication by taking a nap after the meal. This approach is sanctioned by the Rama (Shulchan Aruch Orach Chaim 695:2).
The following is obvious, and I apologize for taking your time with it, but if my blog has any reach at all then I feel an obligation to state this obvious point. Please:
1) Never give alcohol to minors to drink on Purim. It is not necessary for their fulfillment of any Mitzvah. It might be secularly legal as sacramental wine, but it is a foolish and dangerous practice and therefore prohibited as endangering our children as well as violating our obligation of chinuch for our children.
I do believe there is a difference between giving children the barest taste of wine from Kiddush and engaging in Purim drinking in their presence. The former is a formal setting, and no one (I hope) is drinking to get a buzz. On Purim, though, because the drinking is more loose and more geared toward celebration, I believe that the rule should be that children drink no alcohol at all.
2) Adults should not drink on Purim in the presence of young children. Immature children cannot tell when you are in control and when you are not, cannot comprehend the dangers associated with alcohol, cannot accept the idea that adults can do what children are not permitted to do, and cannot understand the difference between Purim and the rest of the year.
Note: When I say young children, the definition depends upon the child. It may well include teenagers; it's a matter of maturity, per #2 above.
The finest joy is a celebration which centers around a Mitzvah, and this is the essence of Purim – the four mitzvot (Megilah, Sending Gifts of Food, Giving to the Poor and having a Feast) which are about experiencing joy and spreading joy and thanking HaShem for saving us from destruction.
For more on this theme see Shaarei Teshuvah of Rav Chaim Margaliyot (printed with a standard Mishneh Berurah), in his final comment on Orach Chaim.
I apologize for wasting anyone’s time by stating the obvious, but as I said above, I feel the responsibility of stating this in any forum I have available.