He is a beautiful bird, but there are lots of friendly, non-aggressive roosters out there that are just as beautiful. I would suggest getting rid of that one, and not replacing him for a while. Let your kids get used to their friendly hens and enjoy them instead. Keep your chickens in a coop with attached run until the hawk gives up and moves on, or only let them out when you're around to keep an eye on things. Often times a dominant hen will take on the role of alerting the flock to danger, just as a rooster would.