@ DWBH....
My approach is not to kick you while you are down, there is always more to a story than anyone will know, so what will be the point of ripping into you? That being said.....
Don't talk about child support with your kids. Just don't do it.
You and your ex appear to have been able, in spite of your problems, to establish a working co-parenting arrangement (?) That means that no matter how you feel about each other and no matter how much you and/or she have moved on, you are still partners with regard to raising your kids.
Additionally, the absolute best thing you can do for your kids right now is work things out with your ex so that you are communicating effectively with each other about money/custody/guilt-trips. That way neither one of you will be tempted to talk through the kids, which your post indicates is where you're headed.
Furthermore, parents use the kids to reach the other parent all the time, and it's just a bad idea all around. Not only does it make the kids feel insecure at home, which is supposed to be the safe place, right? but it also teaches them how to play people, how to manipulate. They already know how you feel about their mom and the situation. They don't need financial details. What they need is for you and your ex to respect them enough to deal with your adult problems without involving them.
Later, when your kid(s) are in high school and they understand more about finances and the decisions behind divorce, they will understand where all their stuff came from and be grateful to you (well, truly grateful might come even later).
Be the bigger person in this situation. If your ex is taking credit for now, let her. It will all come out in the wash later in life. Your 9 yr old doesn't need to hear about all the finances, and I think you will come off looking petty. Suffer now for a big win of gratitude and understanding later and don't get the kids involved.
Finally DWBH, ask yourself this: (a) Will giving the children this piece of information make them better, more generous or responsible people in the end? Or (b) Are you angry about the way your ex-wife manages her money and her business and you want to tell the kids so they'll know this about their mom. If it's (a) then yes if it's (b) then no. From your post, I don't see a lot of (a) but I do see (b).