The news article of July 6, "Paradegoers sickened" talked about free speech, but threats against the president of the United States are not protected speech. It is, in fact, a class D felony under US code Title 18, Section 871 (see http://trac.syr.edu/laws/18/18USC00871.html).
If parents don't respect a president, they should, at least, respect the office and teach their children to do likewise, or if they can't do that, they can maybe suggest that it's generally not a good idea to commit a felony. Respecting the office of the president isn't about being a Republican or a Democrat; it's about being a good citizen. I'm sure it wasn't meant as a real threat but there are things you shouldn't even joke about. In my opinion, this seditious act falls into that category.