Barron is Donald Trump's only child absent from President's address to Congress. Why was he missing?

US President Donald Trump addressed the joint session of Congress today where his entire family was in attendance, except his youngest son Barron Trump. Trump's 18-year-old son was no where to be seen at his joint address to Congress tonight despite Ivanka and Melania being present for the event. But, he gave his father's big speech a miss due to a relatable reason.