My kids are 16 and 13. They saw me drunk enough times to know that I had a problem. My younger son has autism and is nonverbal (he functions at about the level of a 2 year old), so my telling him would have been lost on him for the most part. But I did sit down with my 16 year old and tell him that I was going to AA. He thought it was great. He knew I was an alcoholic before I ever admitted it to him and he thought I was probably hopeless. For him to see me going to meetings and staying sober is huge. Every day he asks me if I "went to AA" and I can happily tell him "yes." It makes his day.
Are you sure your kids don't know that there is something going on with you? They often notice more than we realize they do.