ok, i'm asking because many people must have thought of this. well, at least i'm wondering.
say two minors wanted to have sex. they travel to a state that has the legal consent age of 16, but in their home state the leagal age is 18. can they be charged for having sex in another state? or do people need to follow the laws of the state they were born in, not the laws of the state they were visitng?

There are some issues

1. The laws of the state where the act occurs have jurisdiction no matter what state is your state of residence.

2. Transporting a minor across state lines for the purpose of sexual intercourse and/or without the parents consent or knowledge may be investigated as a "Federal" violation. With both parties being minors, I am uncertain what the outcome would be or how an investigation might play out.

3. Depending on the circumstances, it may violate several other state laws (not sexual offenses) in the state of residence and in the destination state.

A minor is under the legal authority and control of the parents (or legal guardians.) A parent has rights and obligations under the law to act in the best interests of the child’s welfare; to provide for, protect, and control until the age of 18. "Control" means that the child must abide by the laws of the cities and state. If a parent loses this control the juvenile justice system takes control and becomes the child's legal guardian. This is NOT a preferable outcome for any child. Unfortunately, it is the outcome for many.