The Missouri General Assembly recently amended the Minor in Possession statute, RSMo 311.325, so that any person under 21 who attempts to purchase/purchases or possesses alcohol, or who is "visibly in an intoxicated condition" (more on that later) gives implied consent to a chemical test such as a breathalyzer test. This type of "implied consent" is used under the DWI statute to justify suspension of a person's driver's license if they refuse to take a breathalyzer test. So now, a person charged with MIP can also have their license suspended if they refuse to take a breathalyzer test.
Unfortunately, "visibly in an intoxicated condition" gives a police officer wide latitude in citing someone for an MIP, since "intoxicated condition" is defined in RSMo 577.001 as being "under the influence of alcohol." Presumably then, a minor who exhibits any visible of sign of being under the influence of alcohol, no matter how slight, could be cited for an MIP and expected to take a breathalyzer test or face suspension of his or her license.
Hiring a lawyer when charged with an MIP would be highly recommended to protect one's rights, especially considering the driver's license consequences that now accompany the criminal punishments.