Lloyd Prior, 36, was convicted after a trial during which he claimed the complainants were lying about the incidents or misremembering them.
After hearing evidence for two weeks, the jury found Prior guilty of three counts of engaging in sexual activity in the presence of a child, three counts of inciting a child under the age of 13 to engage in sexual activity, and four counts of sexual assault of a child under the age of 13.
Prior, of Broom Knoll, East Bergholt, appeared for sentencing on Wednesday at Chelmsford Crown Court where his victims sat in the public gallery.
A victim impact statement written by the mother of one of the complainants said Prior’s offending led to them suffering from seizures which had been caused by the trauma of his abuse.
She said: “The pain of seeing your child self-harm because of what her abuser did to her is something no mother should have to experience.
“He stole a childhood from her and she was never able to be a normal child and enjoy life.”
Judge Alexander Mills told the court Prior had tried to hide what he was doing by telling his victims not to tell anyone.
He said: “You knew full well what you were doing; you knew it was wrong and you actively took steps to cover it up.”
Prior was jailed for 12 years and ordered to serve a further year on licence.
He has also been ordered to serve a year-long sexual harm prevention order.
