How will they prevent her from going? It's like, how do you prevent a child from running away from home? I guess in this case the authorities could confiscate the boat and eliminate that particular means of escape.
Despite my inapropriate wording, while there is just the INTENTION to break the law, authorities can not take legal action. All they can do is explain that the parent's plan would breach certain laws and that there would be legal consequences.
Only after she actually sets sail can the relevant authorities fine and/or punish the parents for the illegal acts and, depending on the gravity, send a report to another branch of justice to decide if the situation justifies turning her custody to someone else.
In normal countries it is quite difficult to convince a judge that a child should be taken from normal parent's custody, even when their public statements are in support for illegal acts. I believe there is some bluffing going on, probably linked to politics.
