Not just trying to be a puddin' stick here, but I can't help thinking two things.
First, that the boy, being a child, doesn't have rights other than those that devolve from the rights of his parents. And though his dad does have "the right to free speech", egging his child into exercising it in school seems pretty...well, childish. Because...that's not what the boy is at school for.
The point of the exercise was to show patriotism by wearing red, white, and blue, not to front for your dad's political views. I'm sure y'all recall the story from a few weeks ago where a city council (I think) invited a local woman to open a meeting by singing "The Star-Spangled Banner", but she decided to "...express her feelings about being a black woman in America" by singing instead "Lift Every Voice And Sing".
The two stories share a common link, "We asked you to do this and you decided to do that, which makes you wrong." Only difference is, in the little kid's case, his dad can take the blame.