Peter made room and hugged Sirius. He couldn't imagine what it would be like to have your own parents hurt you so much. For all of the problems he had growing up, he always knew that his mother loved him.
"I'm sorry, Sirius. I'm so sorry, but whatever happened, no matter what you did or said, it wasn't your fault. Parents shouldn't do that," he said, squeezing Sirius gently. "It was never your fault and what they did was wrong. They were wrong."
He kissed Sirius' head. "I know that this doesn't make it go away, but maybe you can move forward now, because you never did anything wrong."