http://www.rutherford.org/documents/pdf/brief_bank/E06-CorporalPunishment.pdf.
Parental Rights: Corporal Punishment
INTRODUCTION
Parents generally have the legal right to discipline their children by using reasonable corporal punishment. This right, however, is not absolute and may be subject to scrutiny and restriction by the state.
The questions of whether parents have the right to administer corporal punishment and whether a particular parent has inflicted excessive punishment usually arise in one of two circumstances: (a) criminal prosecution or (b) termination of parental rights.
CRIMINAL PROSECUTION: THE PARENTAL PRIVILEGE
Parents accused of inflicting excessive punishment on their children are sometimes prosecuted for crimes such as assault, battery, child abuse or murder.
The common law recognizes that parents and persons acting in loco parentis (in the place of a parent) have the right to discipline their children by reasonable and timely punishment, including corporal punishment. In other words, if a parent were charged with a crime such as battery, the parent could raise the defense of parental privilege and avoid criminal liability by demonstrating that his use of force against his child was a reasonable exercise of the parental right to discipline.
A vast majority of states continue to recognize the common law rule of parental privilege. Twenty-nine states have expressly incorporated the parental privilege by statute, one of which is North Carolina.
The versions of the privilege vary slightly among the states but not significantly. While the law has traditionally given broad discretion to parents in exercising the parental right to discipline their children, the parental privilege is limited, and exceeding those limits leaves the parent open to criminal liability. The limits of the parental privilege cannot be easily defined but rather are adjudicated on a case-by-case basis and stated in terms such as "reasonable under the circumstances."
Courts deciding criminal appeals that address the limits of the parental privilege usually focus on one of two issues. The first issue addresses who is qualified to assert the privilege. Clearly, parents or guardians with legal custody may assert the privilege in disciplining their own children.
Persons acting in loco parentis may assert the privilege as well. Such persons are individuals who have voluntarily assumed the status of a parent, whether or not through formal legal means.
While it is said that persons acting in loco parentis can discipline a child to the same extent as a parent, some courts do not give persons acting in loco parentis the same latitude in discretion to punish.
The states have traditionally offered the parental privilege to teachers as well, although some states in recent years have withdrawn that protection. The second and more recurrent issue addressed by the courts is what constitutes reasonable punishment and, more importantly, what punishment exceeds what is reasonable.
In determining reasonableness, the law considers all of the circumstances surrounding the punishment, including the age and physical condition of the child, the severity of the punishment inflicted on the child and the gravity of the offense committed by the child. A cursory review of the cases indicates that the courts are very deferential to moderate spankings on the buttocks but are more suspicious when permanent injuries or scars are inflicted, when objects such as glass bottles and baseball bats are used and when episodes of beatings continue for prolonged periods of time.
The question of whether a parent's disciplinary action is reasonable is a question for the jury. A defendant's conviction will not be overturned on appeal unless there is no evidence to support the jury's verdict.
Summary:
So, yes, in North Carolina, a step-parent acting "as a parent" in a caregiver situation, may administer reasonable punishment to your child without fear of legal reprisal.
IAAL