The non custodial party walked away 8 years ago after the divorce was final. Now he wants to start seeing the kids who are 17 and 10 again. He had visitation but chose not to see them. What can I do as the custodial party to keep him from the kids?

Go back to court and ask that the visitation order be dropped. But don't be surprised if the court grants visitation at some level.

You can as noted file in court, but I doubt they will allow no visits, he will show he has changed, you at best will get them to order counseling for the kids ( he pays for) and supervised visits to begin with.