Of course she doesn't believe you when you say you can change. Have you said it before? And did you follow through?
One of the guidelines we follow here is to believe none of what the WAS says and only half of what they do. Words mean nothing, only action.
Do not tell her what you are doing. Just show her. And do not go out of your way to point out your actions. Just do it. She will notice. She may not say anything but she will notice.
You think it would be easier without children, people without children think it would easier with them to have a bond to their WAS. It's moot. Just be the best father you can be and do not involve them in this.
Have you read DR yet?
If you love somebody, set them free. http://tinyurl.com/2empx2g