I hope you don't mind, but I spoke to my friend this morning about your situation to try to get some more information for you.
The first thing he mentioned was the depression that came with quitting. By facing up to your addiction, you are in essence trying to erase of part of you that you no longer wish to know. This caused him the greatest amount of depression. He battled the depression and the mood swings with exercise as excercise releases endorphins ("depression killing chemical" as he called them). He didn't do anything too strenuous - a walk, a run, cleaning the house. But something to take his mind off the cravings and pull him out of the mood he was in. He said that you don't necessarily need to do this, but without physical activity, you will find quitting much more difficult.
He mentioned those who slowly cut back their usage prior to quitting completely and mentioned that, even though this may seem like the easier way to do it, it is prolonging the inevitable and causes greater cravings than simply quitting "cold turkey".
You also need to make sure that everyone in your life is aware of your decision to quit and that they support you in this decision. If you have friends who you smoke with, unless they are able to support you fully - you are probably better without them in your life. My friend said he severed ties with numerous friends who he used to get high with as they continually offered him weed after his quit date.
Finally, he opened a savings account where he deposited all the money he would have spent on weed or other drugs. After three years sober his balance is over £10,000 (and he says he has withdrawn from the account numerous times over the years). For him, this became a prime reason to maintain his sobriety. This is his "fun money" to buy things that he has always wanted but could never previously afford because of his various addictions.
He has highly recommended this site. It is Australian, but he said it has been a huge help in quitting and maintaining his quit. I hope it is as helpful to you as it was to him.
You already know all of the reasons for quitting. I know you are pretty low at the moment, but you need to find the strength to do this - for your sake as well as your children.
If you ever need to talk, I am more than happy for you to email me. No pressure, only if you want to anniebeansmum AT yahoo DOT co DOT uk. Good luck - you CAN do this!