I cannot even begin how very very very very strongly I disagree with this above post.
OMG....
I don't care if these were actually HER kids.. (and not step-kids)
Just because one is a wife and mother does not mean that you are a servant, on call, 24/7.
Being born with a female body part does not mean that you are a 24/7 life-long servant... and it is ASSUMED that you are always there to care-for and to do-for the males and the children.
And, whether one wants to be a 'hater' and flame this woman because they are not their kids... or not... The fact remains that these kids have TWO biological parents who simply assumed that she would take the time off and give up her break so THEY wouldn't have to.
Unbelievable that there are still women, who are not in some third-world country, who not only adhere to this mind-set, but would openly hate and judge any who do not.
OP, you need to talk with your husband.
You need to start to establish a new status-quo and more healthy respect and boundaries...
Shared responsibility... Breaks for you... etc.
Again, HUGS!!!!