Yes it is a crime, although it is not frequently charged at least from what I have seen in the DWI cases I have handled. That being said if you fight the case they can always bring this up and charge you if you were not charged before. Thus if you have a DWI and children were present, I suggest you get a good lawyer. Most of is criminal lawyer offer a free in office consultation, I suggest you set one up ASAP.
§ 2C:24-4. Endangering the Welfare of a Child
Any person having a legal duty for the care of a child or who has assumed responsibility for the care of a child who engages in sexual conduct which would impair or debauch the morals of the child, or who causes the child harm that would make the child an abused or neglected child as defined in R.S. 9:6-1, R.S. 9:6-3 and P.L. 1974, c. 119, § 1 is guilty of a crime of the second degree. Any other person who engages in conduct or who causes harm as described in this subsection to a child under the age of 16 is guilty of a crime of the third degree.
DWI with children in the vehicle can result in a serious indictable crime. A second degree crime is punishable by five (5) to ten (10) years in New Jersey state prison and there is a presumption of incarceration (meaning a minimum five (5) year prison sentence) even if you have no prior criminal record.
