Only in very specific cases:

For parents of a child, it is only a crime for these cases:

Noncustodial parents; 
Fathers whose paternity the government hasn't recognized; 
Parents in active custody cases; 
Parents with a court order requiring them to do so; 

In general, though, you don’t need explicit permission to take your child out of state.

For non-parents, it is only illegal if done for the following purposes:

Transportation With Intent To Engage in Criminal Sexual Activity;
Travel With Intent To Engage in Illicit Sexual Conduct; 
Engaging in Illicit Sexual Conduct in Foreign Places; 
Illicit Sexual Conduct in Connection With Certain Organizations; 
Ancillary Offenses (to sexual misconduct);

Attempt and Conspiracy (to those acts above);

It’s weird that noncustodial parents are more restricted on taking kids out of state than random non-parental people.