Yes, Gandhi slept with girls naked as a part of sexual experiments on attaining celibacy when he was 70 years old. The girls were Manu (Gandhi's grandniece), Abha (wife of Gandhi's nephew Kanu) and Sushila Nayar (younger sister of Gandhi's personal secretary Pyarelal).
In his 70s, in the sunset of his life, Gandhi embarked on a new set of sexual experiments in which several women partook, among them Manu and Abha, his “two walking sticks”, and Sushila Nayar, his personal physician and sister of his secretary Pyarelal. In the midst of raging communal violence, which Gandhi characteristically attributed to his own personal shortcomings, he decided to test his resolve – by going to bed naked with one or the other of the women. Source: The Sexuality of a Celibate Life
Also referring to the diaries by Mridula Gandhi or Manuben which is mentioned here, here and here, there is further confirmation from one of the participants that Gandhi's sexuality experiments took place.
Bapu has told his followers during the morning prayer that he was carrying out celibacy experiments with me. Then he explained to me why he spoke about it. I felt very relieved as it will stop tongues from wagging. I told myself I don't care now. Let the world say whatever it wants. Source: Excerpts from Manuben diaries