It depends on the circunstances of each case.
In Brazil, I see difficulties on classifying Bruna's actions as crime of kidnapping, according to the brazilian criminal law. The crime of kidnapping is related to the restriction of the victim's locomotion, easily visualized when we imagine a person locked inside a small and dark room, awaiting for the payment of the ransom, unable to leave the room.
Bruna took Sean to Brasil. Although he didn't have his father presence, except for that, he was having a "normal" life, going to school, to the park, cinema, beach, playing with friends, doing sports, etc. He could go to anywhere, except to USA, of course. Even so, I think it's very difficult to imagine a judge that would classify all of this as a crime of kidnapping. But maybe there's a judge somewhere that believes it's a kidnapping crime.
Course I think that not having a father is not normal. I mean "normal" because he was not in a similar situation that the person I mentioned above, locked in a small and dark room.
Also the Hague Convention is about the Civil Aspects of the international child abduction. It can not be used to file criminal charges against the "abductor" parent. If a country wants to do that, it needs to use another legal document, it needs to create a criminal law/act, in order to prosecute the parent, or use an existing one. Note that unlawful does not necessarily mean crime. The crime is a kind of illicit, it's the worst kind of illicit, which is punished with jail (in some countries, also with the death penalty).
And, I bet that +90% of the Familiy/International Law experts envolved on the creation of the Convention, and the others law experts around the world, and considering that the parent did not comitted other unlawful conduct except the wrong remmoval of the child, would think that applying Criminal Law in these cases is not a good solution.
Remember, all of this, the Hague Convention and the internal laws of each country are based on the best interests of the child, and having one of the parents locked in jail is not on the best interest of the child. The judges would consider it a Family Law issue, and not a Criminal Law issue. The best solution is solving the case, in order to maintain the presence of both parents in the child's life. We can also imagine a situation where the only thing that prevents an "abductor" parent to return with the child to the child's previous habitual residence is the threat of being arrested.
I think that Criminal Law should be applied in very especific situations, and not be considered as a rule over Hague cases.