How should I punish my kids?

I left my 3 kids alone for about an hour. I have 12 year old twins and a 10 year old boy. So while I was out I guess my 12 year old twins thought it would be cool to cut their little brothers hair. It looks awful and I don't really know what to do. I'm going to take my 10 year old son tomorrow to the barber shop so they can fix his hair. But what should I do to my 12 year old sons? I can't trust them alone anymore. How should I punish them?? Nothing like beating the kids or anything with hurting them.