Dear OP, first of all I am very sorry that you are going through this. None of us gets married planning on getting a divorce down the road, we all believe that this is going to be forever. However, some marriages simply do not work out. Do not feel bad about that. You need to listen to yourself, your instincts, your feelings. I do not think that a divorce "destroys" anything, it is not a "disaster". Your relationship has simply ran its course and you are going separate ways.
As for the children, here is what I think. Kids are smart and intuitive and they can sense when things are not ok between the parents. They may not want you to get divorce but they want you to be happy. So, whatever you think about your divorce, and what/how you tell them, will affect how they feel about it. I just went through a separation and while my kids are much older then yours I strongly believe that this is the way to go when it comes to telling them. You sit them down, preferably both you and your husband and tell them this: "Your father and I are separating. We have had some problems over the years and we tried to fix them but we could not. We need you to know that this has nothing to do with you and that we both love you very, very much". That is all. The kids do not need to know the details of your relationship with your husband, the kinds of problems you had and how you tried to fix it. All they need to know are the fact, "we are separating", "we love you very much". It would be useful if you know, more or less, the arrangements regarding who they will live with and such. In my case, I told them that I will stay in the house with them and that they do not have to go anywhere, but that they can chose to go with their father if they wanted to.
Bottom line is, while you should be emotional as this is a major event for all of you, do not catastrophize it. Stay calm and composed. Kids will be looking at you for signs. They need to know that you know what you are doing and that everything is going to be ok. Kids need love and stability and as long as you can give it to them they will be ok. Good luck OP. Hugs 