The documentation required by international or non-United States students has always been extensive. As I have pointed out many times, if you are not an American citizen and are living outside the United States of America, and you wish to attend a boarding school in the U.S., you need to start the process at least 18 months in advance of the date of your first class. See the College Application Timeline on International Student for a detailed timeline. While the article discusses how to apply to American universities, the process is the same for students applying to American private K-12 schools
What is being adhered to more strictly is a policy which dates back to the Obama administration. This policy requires that applicants for U.S. visas furnish their social media usernames. U.S. Requiring Social Media Information From Visa Applicants in the New York Times gives an overview of the changes. An update to the Privacy Act of 1974; System of Records was published on September 18, 2017. Specifically, it adds the following clause: "Social media handles and aliases, associated identifiable information, and search results"
This video discusses how the US Border Patrol now requires all immigrants to provide social media logins and passwords, phone records going back 5 years, and other details.
How does this impact your child's student visa application?