Sorry you and your husband have reached the point of seperating...hopefully one day you'll get back together.
In the meantime I want to congratulate you and your husband on how you are dealing with the children..
I tend to think you are doing a great job in terms of this with the children. Keep communicating with them...
The more they communicate their feelings, the better it is for them. If there is any cover up, you'd probably notice it first in change of behaviors.
Ask them to draw and color pictures for you..."fridge art"....young children communicate well in their drawings and in the colors they choose to use.
Some children of separated parents might draw houses and family members...leaving out one family member...or putting a family member off in a cornor on the sheet of paper while the others are grouped together....and sometimes they will use muddy colors instead of bright colorful ones...In anycase if you do decide to try this, talk to them about their creative work...ask questions, allowing them to explain in their own words what their picture is about. Most of the time a happy child would have a lengthy happy story to tell about their picture. An unhappy child might not even want to talk about the picture...might even take to coloring over it.. You know your children best, see how it goes.
Since you are a working Mom, have you talked to their teachers about the change in the family unity. Thinking since they spend a good part of the day with your children, they can observe and keep you informed of any changes in behavior or grades droping...
Take care and keep us posted....