The 52-year-old has been at the centre of wild rumours this week that wife Angelina Jolie, 41, filed for divorce because of differences over their style of parenting.
There have been unconfirmed allegations of a row between Brad and teenage son Maddox, 15, on a private jet with some outlets claiming that triggered Angelina's decision to file for divorce.
The Los Angeles Police Department have denied allegations they were investigating Brad for child abuse, but the FBI has suggested they're still looking into the alleged incident onboard the plane.
An FBI statement read: "In response to your inquiry regarding allegations within the special aircraft jurisdiction of the United States; specifically, an aircraft carrying Mr. Brad Pitt and his children, the FBI is continuing to gather facts and will evaluate whether an investigation at the federal level will be pursued."
Neither Brad nor Angelina has commented on the latest development but sources have said Brad's fully co-operating with the investigation.
The Sun is claiming Brad and Maddox rowed during a flight from France to the US, but anonymous staff members of the Jolie-Pitt household told the newspaper it's been blown out of proportion and Brad is a loving, caring father.
One staff member, who remained anonymous, said: "Brad feels terrible for the kids. He also feels that what is being said about him isn't accurate and fair. I don't believe it is either... He's kind and really nice with the kids. Brad is an easy-going guy. He's a good father."
Another insider said: "[Brad] was not physical in any way that has been reported. He will always do whatever is best for his kids."
Angelina filed for divorce from Brad on 19 September citing irreconcilable differences. It's believed she's requested full custody of their six children with Brad having visitation rights. They're parents to Maddox, Pax, 12, Zahara, 11, Shiloh, 10, and twins Vivienne and Knox, eight.
A statement released by Angelina's lawyer when she filed the papers said: "This decision was made for the health of the family. She will not be commenting at this time, and asks that the family be given their privacy during this difficult time."
Brad later responded with his own brief statement, simply saying: "I am very saddened by this, but what matters most now is the well-being of our kids."
The couple met while playing married assassins in the action movie Mr and Mrs Smith back in 2005 and married at their French chateau in 2014.