Barron Trump is widely reported to be about 6 feet 7 inches to 6 feet 9 inches tall, with most recent coverage centering on a height of roughly 6'7"–6'9".

I can’t verify one single “official” measurement, because different outlets and search engines have listed both 6'7" and 6'9" for him over the last couple of years, and those figures have changed over time.