I don't have kids, so don't have much footing in terms of weighing in on the matter, but I think short of preventing your children from seeing it... honestly is always the best policy right? Your husband is going with right? Maybe you guys can all go out for ice cream (or whatever) after it and talk about what you think/feel?
I remember my mom wouldn't let me see Dirty Dancing when it first came out b/c of the abortion content. I did of course eventually see it at a friends house - where her mom fast forwarded through the scenes she thought were inappropriate. In reality, I don't know that my mom was really 'protecting' me from much of anything... (I knew what abortion was, etc.) Granted, the two movies are entirely different genres.
Now I did read some pretty seedy novels as a youngster that I wish in hindsight I hadn't read...
And I remember wanting to read or see a special on child abuse that my dad ABSOLUTELY refused to let me watch (in his quiet, Ennis way). And I am glad for that.
Maybe it would be helpful to talk with your sons about the anticipated darkness of the movie? Or are they like "yeah mom, whatever"?

Thanks for your input, it is much appreciated. I have discussed TDK at length with both of them. The younger one just says it's not real is it,I am only scared when it is someting that could really happen.The older one will watch it come what may. In many ways I am more concerned about him. He has such dark thoughts anyway, and I suspect he will get the undertones and implications.
If I had been warned in advance, how difficult this parenting thing is, I might have given it a miss.
I am gong to suggest to my husband that we skip the 12.01am showing, and buy new ones for a day show.That way my daughter an I could go shopping, meet up with them after the film for an ice cream or drink. The boys could then air their opinions so get it all out in the open.But most of all we would be leaving the cinema and mall in daylight.
So once again thanks, that was a really good suggestion of yours. I am going to stick my foot down about the midnight showing.They would arrive in the dark, leave in the dark and then go to bed.
The meeting up for an icecream and discussion in the daylight is a much better idea.