L.B.
Hi K.,
I've definitely been where you are in years past. My advice to you would be to make it perfectly clear up front during the interview process that you are a mother first then you will give their company your 100% during your hours of work. Explain that you need to be off at a certain hour and also let them know if you are the person who will have to leave early or stay home if your children are ill. Add that you will take time off without pay if necessary.
I believe there are lists on the internet of the best companies to work for, by state and some of the working women magazine sites have them.
I think that honesty is the best approach right from the start with everyone you interview with and don't be afraid to remind folks of the conversations you had if necessary. If a company is going to judge you first on your family priorities and not your credentials, they aren't someone you want to work for anyway.
Good luck!