The prison time isn't for violation of "no contact"--it was for an extremely brutal assault. About the only virtue of a plea is to spare the kids from having to testify.
A "no contact" condition as part of a sentence only applies while the defendant is subject to court (or parole) supervision. Once that time is up, it's up. If one of those conditions is violated, the court or the parole board can usually order the defendant back to prison to serve the rest of his sentence.
But a civil protection order can be of indefinite duration. Which is why, even if the court orders no contact as part of the sentence in the criminal case it's a good idea to get a civil protective order as well.