Traveling on business and on my BB, so more later this weekend but some quick thoughts.
First, agree 100% with H on not blaming anyone to the kids. They need both of you badly. For them, avoid having them blame anyone.
Second, I will email you (later) my detailed journal entry on how we told the kids. You can use it as a guide. We consulted with a child psychologist on it. I think my kids are about the same age as yours. (I sent it to N_A previously, so maybe she can send it to you before I get back home.)
Third, you should tell the kids only a few days before you implement the S. They shouldn't be able to worry about it happening for weeks. We told ours on a Sat, and it started on a Mon. We cleared the whole weekend so we could both be there for them and spend lots of time with them.
Hope it helps, Nomo
M 39 W 39 M'd 10 yrs; T 14 yrs S7 D4 Bomb 5-8-05 W not working on M 1-22-07; EA 2-22 DB 4-10 S 6-11 No more C Link