Assuming that you didn’t leave out anything significant then it would appear you have a good defense to the charge. The statute for contributing to the delinquency of a minor is Tenn. Code. § 37-1-156(a)(1):
Any adult who contributes to or encourages the delinquency or unruly behavior of a child, whether by aiding or abetting or encouraging the child in the commission of an act of delinquency or unruly conduct or by participating as a principal with the child in an act of delinquency, unruly conduct or by aiding the child in concealing an act of delinquency or unruly conduct following its commission, commits a Class A misdemeanor, triable in the circuit or criminal court.
So, the minor has to be involved in an act of delinquency or unruly behavior and you have to somehow contribute to the minor doing that to be guilty of the offense. The definition of “delinquent act” is in Tenn. Code § 37-1-102(b)(9):
“Delinquent act” means an act designated a crime under the law, including local ordinances of this state, or of another state if the act occurred in that state, or under federal law, and the crime is not a status offense under subdivision (b)(23)(A)(iii) and the crime is not a traffic offense as defined in the traffic code of the state other than failing to stop when involved in an accident pursuant to § 55-10-101, driving while under the influence of an intoxicant or drug, vehicular homicide or any other traffic offense classified as a felony.
(Bolding added.) So, I’m guessing that the officer may have known that if the minor commits a criminal act and you contribute to that act that you are contributing to the delinquency a minor but may not have known or remembered that the law excludes most non-felony traffic offenses from that. Thus, if your brother’s only violation here was driving without a license, which is non-felony traffic violation, he would not have been engaged in a delinquent act and that would not be a proper basis for citing you for the offense.
Next, let’s look at the definition of “unruly child” in Tenn. Code § 37-1-102(b)(23):
“Unruly child” means a child in need of treatment and rehabilitation who:
(A) Habitually and without justification is truant from school while subject to compulsory school attendance under § 49-6-3007;
(B) Habitually is disobedient of the reasonable and lawful commands of the child's parent(s), guardian or other legal custodian to the degree that such child's health and safety are endangered;
(C) Commits an offense that is applicable only to a child; or
(D) Is away from the home, residence or any other residential placement of the child's parent(s), guardian or other legal custodian without their consent. Such child shall be known and defined as a “runaway”.
None of those seem to fit here either. Unless the state is going to try to claim your brother was a “runaway” he was not an unruly child, so contributing to him being an unruly child that would not be a basis for citing you for the offense, either.
I suggest you get a lawyer to represent you on this. A good one can probably make this go away pretty quickly unless there is more to this than you have stated here. That shouldn’t cost all that much. Once the prosecutor realizes that a traffic offense is the basis of the claimed delinquent act he/she won’t want to pursue this because the court will simply dismiss it on a proper motion anyway. This assumes that your brother did not leave the scene of the accident before the cops showed up. If he did leave the scene of the accident, then you may still have a defense to this but it will be more complex and thus even more reason to have an attorney on board. You do not want to have a misdemeanor criminal conviction against you even if you can avoid jail time if you can help it.