Good question..... I had the same issue, though my kids are a little older. I decided to listen to my intuition for when it was the right time to say something to them. Basically I told them that I was getting too attached to drinking and had decided to stop. I didn't go into a lot of nitty gritty detail, but I did talk a little about addiction and what alcohol really does to us and that I want them to come to me if they ever see it becoming a problem for them.
I don't know your children well enough, but it seems to me that at 10 and 13, they would understand. The 13 year-old could already be faced with alcohol and drugs at school - mine were.....