i have to agree with HFF but only up to a point. You certainly must have the conversation with the children together, BUT even though it is the W's decision to get the divorce you have to be careful to not bash her in front of the children. They will learn the truth eventually of the entire situation and they will form their own opinions about their mother.
If you both sit down and talk to them about it but there is obvious anger in your voice and you are outright blaming her, they will be very upset. They are going to have very negative feelings about their mother right off the bat. i don't think that is fair to a 3 and 7 year old. They are just too young and it's not fair.
I agree that they eventually need to know that it was mom's choice but they are going to be devasted enough right now and need to know that they can go to either parent for love and support. Mom is not divorcing them she is divorcing dad.
it just needs to be handled delicately for their sake. This conversation is not the conversation to vindicate you no matter how hurt and angry you might be. JMHO as a mom.
Life is not measured by the number of breaths we take,rather by the moments that take our breath away. M38,H40 M14 K D11 S8 D - June 09