NBC further reports the letter was addressed to Donald Trump Jr.
It is believed that nobody suffered any injuries and no sign that the substance was a hazardous material. Three people at the Trump residence were taken to New York Presbyterian-Well Cornwell Medical Centre.
Trump Jr and Vanessa have been married since 2005 and share five children - daughters Kai, 10 and Chloe, 3, and sons Donald III, 8, Tristan, 6, and Spencer, 5.