How do you....

How do you explain to your children the journey we are all about to be on? I have a 15 year old, 7 year old, and 4 year old. I haven't really told them what is going on but I feel it is a conversation we need to have. I have my consult and seminar Tuesday 2/4 and after that it's on the way so I wanted to make sure to communicate somehow the changes and appts and such. I know it will have to be adjusted for each of them due to their ages, but anyone have any advice?  Not telling them or lying is not an option for me.