"I do not agree with the procedure that aims to separate parents from their children. I do not know if they have a possibility to do it differently in the United States… But I am going to tell the truth now: the parents are the ones responsible for the situation," Le Pen told France 2 broadcaster.
Le Pen noted that the politicians who "encourage" undocumented migrants to cross the border were also to blame.
The separations began after US Attorney General Jeff Sessions announced a new zero-tolerance policy on illegal immigration in April.
Le Pen's party, RN (formerly National Front) is well-known for its tough stance on immigration. In 2017, Le Pen ran for French presidency pledging to introduce immigration quotas and tighten the conditions for obtaining citizenship. She lost to a centrist candidate, Emmanuel Macron.