That we are seperating/divorcing. I don't know that they need to know about the A at their age.
Children at 7 & 5 yrs of age do not understand all that trash. However, you need to be there as your "wife" explains to the children how "she" has chosen not to live together. Do not allow her to make it all sound as if this is a mutual agreement and all will be honky-dory. You have her to break the news to the children....but you make sure she tells it right!
But.....they aren't going to understand any of it anyway. That is the pitiful part of all this! All they know is that everyone seems to be unhappy and upset. Their world is turned over and they don't know why. They will need more love and more time with their father than ever before. You have to take a big gulp of air and be the man they need to walk before them. Forget about your nerves and fear and all of that (and I'm not saying this in a sarcastic way), and keep your love for them ever in your eyes and tone of voice. You keep things under control and in order, and do not allow tempers to flare before these babies.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!