There is no need to tell them anything other than that they are being dismissed and the terms of that dismissal. That's your lead into any discussion and any attempts to sugar coat it are misguided.
When I was let go, I had received a phone call about 10min prior from another employee that was out of the same depot I was. He said he'd been let go and if I could grab some papers for him he would appreciate it, adding that the boss was at the depot waiting for me. Then and there I knew I was going to be let go too, but why is a whole other story.
I showed up, saw the cars in the lot and again I knew. I walked in the office and saw a 2nd manager (knowing when 2 are present it's for legal reasons) it was confirmed. I went to the bathroom and as I came out my boss said "Have a seat." I told him 'Cut to the chase, I'm laid off aren't I?' and he continued and stressed for me to sit down again. As I sat down I told him 'I asked you once, don't sugarcoat anything or continue to piss me off me and betray me, I don't have a job as I walk out of this office, right?'
Not all employees take it that way though. Of the 4 of us laid off that day, one didn't know any better, I took it as I was given, another knew he was toast because I called him with a heads up and the other one (the worst employee of the lot, go figure) went ballistic.