"Thankful that Vanessa & my children are safe and unharmed after the incredibly scary situation that occurred this morning. Truly disgusting that certain individuals choose to express their opposing views with such disturbing behavior," Trump Jr. wrote on Twitter.
The US Secret Service in a statement on Monday confirmed that it was investigating into a suspicious package in New York City which had been addressed to one of the individuals under its protection.
In 2001, several US officials received envelopes containing anthrax spores. As a result of the high-profile attacks, five people were killed and around 20 others infected.