Jenny I've just started reading this thread and I'm so sorry for how you're feeling. Not only do you have to cope with your own personal grief at losing your partner, and your love, but you have to deal with the confusion and grief of your children, too.
I cannot fathom the pain and difficulties you must be going through. I truly believe that anyone who has children at all faces some life-changing challenges and obstacles, but that someone who has additional hardship to endure must have a very, very tough time.
I don't really have any advice that I feel would be useful to you, as I don't have the slightest idea what it must feel like to be you at the moment, but I can say that the fact that you are searching for answers, and help, and advice, must mean that you are a very committed, loving and dedicated parent. Your children and you will band together, and become such a strong unit, because of your open and loving attitude.
I can't say I don't think there will be many more lonely, sad and difficult times for you as your children grow, and you feel more keenly the loss of your husband, but I CAN say for sure that you will just grow stronger, and more understanding, and more compassionate, and more experienced, and that you will overcome the hurdles that seem insurmountable when they arrive, just as you will overcome this one.
My heart goes out to you, and my thoughts and best wishes, and I hope that you and your children find comfort in one another, to help you through your grief and sadness, and that each day the loving memory of your husband and their father will bring you a smile.