Leslie Van Houten deserves parole from her life sentence because she was too immature to understand her savage actions in the Manson family killing spree according to new legal docs.

Leslie’s lawyer, Richard Pfeiffer, submitted a 13-page report to convince the parole board to release her. The report includes testimony from psychologist Laurence Steinberg ... who says then 19-year-old Leslie’s immaturity prevented her from exercising self-restraint, controlling her impulses and weighing consequences.

Van Houten was convicted for the stabbing murders of Leno and Rosemary LaBianca.

Steinberg adds as Van Houten grew up ... her brain matured and she escaped Charles Manson’s brainwashing. He believes her exemplary prison record proves she has matured and “strongly suggests” she won’t commit further criminal acts.

Of course, Van Houten got shot down for parole last year when Governor Jerry Brown nixed the idea. The report will be presented at her next parole hearing, later this year.

Leslie, now 67, was the youngest person ever sentenced to death in California. That was later commuted to life with parole.