It is pretty well agreed upon by the professionals that the earlier you tell the children the better. Most people hold off for months, even years, while they no longer share a bedroom, etc., believing the children are not catching on the the “change” in the house. The reality is they ARE catching on and when they are not told what is really going on they will make it up themselves. And as you can imagine, what they make up will be far worse than the truth and will likely involve them as the guilty party for breaking up their parents.
Grab a book and do some research and tell the children…sooner rather than later.