First, I sympathise with you, and your children....
I am a single Dad, have been for 8 years now.
If your husband has any self respect, and love for your children - which I am sure he has, then he needs to tell the children what he intends to do.
You both need to be there and show the kids that you both still love them, as Mum and Dad, because you will always be their Mum and Dad .... no matter what, and tell them together. It will be painfull. Very painfull.
Let the kids ask questions and answer them as best you can.
Maybe they will show anger, contempt, fear, disappointment ......... you need to be strong.
There is soooooo much more I could say, but, I will leave it here.
You are welcome to get in touch if you need a shoulder to lean on, or someone to yell at.
Through your love, and strength, your kids will grow and thrive - believe me.
Good luck and my best wishes go out to you. Don