18-yr son arrested for minor consumption & resisting arrest. Do I need to obtain an attorney? first offense

Yes, because even though the minor consumption of alcohol (in the grand scheme of crimes) may not be as bad, the resisting arrest is really bad.  Better to obtain an attorney now, especially if both of these charges are first offenses. Your son needs a criminal defense attorney to ensure the most advantageous outcome for your son.  Try www.attorneypages.com and also cross check the attorney with your state bar.

Here are some items to review:

1.

IC 7.1-5-7-72.
Illegal possession
     Sec. 7. (a) It is a Class C misdemeanor for a minor to knowingly:
        (1) possess an alcoholic beverage;
        (2) consume it; or
        (3) transport it on a public highway when not accompanied by at least one (1) of his parents or guardians.
    (b) If a minor is found to have violated subsection (a) while operating a motor vehicle, the court may order the minor's driver's license suspended for up to one (1) year. However, if the minor is less than eighteen (18) years of age, the court shall order the minor's driver's license suspended for at least sixty (60) days.
    (c) The court shall deliver any order suspending the minor's driver's license under this section to the bureau of motor vehicles, which shall suspend the minor's driver's license under IC 9-24-18-12 for the period ordered by the court.
(Formerly: Acts 1973, P.L.55, SEC.1.) As amended by Acts 1978, P.L.2, SEC.710; Acts 1982, P.L.69, SEC.15; P.L.53-1994, SEC.1.

IC 35-44-3-3
Resisting law enforcement; mandatory sentence
     Sec. 3. (a) A person who knowingly or intentionally:
        (1) forcibly resists, obstructs, or interferes with a law enforcement officer or a person assisting the officer while the officer is lawfully engaged in the execution of the officer's duties;
        (2) forcibly resists, obstructs, or interferes with the authorized service or execution of a civil or criminal process or order of a court; or
        (3) flees from a law enforcement officer after the officer has, by visible or audible means, including operation of the law enforcement officer's siren or emergency lights, identified himself or herself and ordered the person to stop;
commits resisting law enforcement, a Class A misdemeanor, except as provided in subsection (b).
    (b) The offense under subsection (a) is a:
        (1) Class D felony if:
            (A) the offense is described in subsection (a)(3) and the person uses a vehicle to commit the offense; or
            (B) while committing any offense described in subsection (a), the person draws or uses a deadly weapon, inflicts bodily injury on or otherwise causes bodily injury to another person, or operates a vehicle in a manner that creates a substantial risk of bodily injury to another person;
        (2) Class C felony if, while committing any offense described

in subsection (a), the person operates a vehicle in a manner that causes serious bodily injury to another person; and
        (3) Class B felony if, while committing any offense described in subsection (a), the person operates a vehicle in a manner that causes the death of another person.
    (c) For purposes of this section, a law enforcement officer includes an enforcement officer of the alcohol and tobacco commission and a conservation officer of the department of natural resources.
    (d) If a person uses a vehicle to commit a felony offense under subsection (b)(1)(B), (b)(2), or (b)(3), as part of the criminal penalty imposed for the offense, the court shall impose a minimum executed sentence of at least:
        (1) thirty (30) days, if the person does not have a prior unrelated conviction under this section;
        (2) one hundred eighty (180) days, if the person has one (1) prior unrelated conviction under this section; or
        (3) one (1) year, if the person has two (2) or more prior unrelated convictions under this section.
    (e) Notwithstanding IC 35-50-2-2 and IC 35-50-3-1, the mandatory minimum sentence imposed under subsection (d) may not be suspended.
As added by Acts 1976, P.L.148, SEC.4. Amended by Acts 1977, P.L.340, SEC.61; Acts 1979, P.L.83, SEC.11; P.L.188-1984, SEC.1; P.L.325-1987, SEC.1; P.L.248-1993, SEC.1; P.L.13-1998, SEC.1; P.L.143-2006, SEC.2.

3. http://www.in.gov/legislative/ic/code/title35/ar50/