Peter Robbins, 56, pleaded guilty on Wednesday in a San Diego court to threatening and stalking his ex-girlfriend and a plastic surgeon who gave her a breast enhancement.
He called his former girlfriend, Shawna Kern, dozens of times a day and told her he would kill her and her son if she did not give back his dog and car.
Kern, a Los Angeles resident, told investigators that she and Robbins got into a fight during which he grabbed her by the neck and demanded that she go with him to get back the money he paid for the breast enhancement.
Their relationship ended after that incident, but authorities say Robbins left several threatening phone messages for Kern, saying in one, "You better hide, Shawna. I'm coming for you. I'm going to find you in Sun Valley or wherever the (expletive) you live and I'm going to kill you."
Prosecutors say Robins made threats against the surgeon, Dr. Lori Saltz, as well.
According to Deputy District Attorney Elizabeth McClutchey, Robbins had purchased a gun, though he had yet to receive it, and practiced shooting at a firing range.
Robbins will be sentenced next month. He faces up to three years in prison.
Robbins was 9 years old when he began doing vocal performances for such films and television specials as "A Boy Named Charlie Brown," "A Charlie Brown Christmas" and "It's the Great Pumpkin, Charlie Brown."
The Associated Press and City News Service contributed to this report.