Actually, I need to update my profile, my kids are both 6. But I don't think there is a "good age" to do that to a child.
Hopefully, your working with the script will work. I tried that and my wife just blasted through it, like there wouldn't be any problems. Even if I presented such she'd just give a generic "not your fault" "we still love you very much" response.
Also, remember that just like any scripted conversation, reality doesn't always go the way we'd hoped. Be careful not to script in your own head your wifes response to the script. (I hope that made sense).