Yes Robin Williams is divorcing his second wife who was indeed the nanny for his son from his first marriage. She then became Robin's personal assistant and then-- ta-da-- his wife.
It is sweet and considerate and very important that they are keeping a lid on the animosity for the sake of their children. We all try to do that, and we often fail. We recommend that you bite your tongue when discussing your ex with the children.
Remember your mother’s age-old advice when you talk to the kids about Dad’s shenanigans: “If you don’t have anything nice to say, don’t say it.” We would add, “Lie through your teeth instead.” Then give yourself a pat on the back for being a great mom.