I have three kids, ages 12, 14 and 16. For many years I was a single mom and had to work. My new husband is disabled and is very limited in his work so I still have to work full time. I work overtime right now. It is difficult, but necessary to care for my family. This is my advice to you:
Employ extended family. Yes, no one can replace mom, but I have my mother living with us (we take care of her) and my husband works substantially fewer hours than I do. He and I tag team on the parenting (even though he is a step father, he is wonderful). He gets the kids to appointments and helps with the duties. My mother helps tremendously too.
Is your new job "family friendly?" My job allows me time to take off for school programs and kids' activities as well as illnesses. They also allow me to take calls from my kids and to call them.
Is there anything that you can do from your home? I do a lot of freelance writing. If you can write you can easily make $500 to $600 or more per week. It takes discipline and motivation but it can be done. There are also a lot of jobs out there for transcriptionists, proofreaders and other opportunities. I mentor several writers and am helping them learn how to freelance and write so that they can sustain themselves. If you would like to talk about it you can PM me and I will give you more information and tell you where to go to find projects. I just do it to help these women because they may have self esteem issues or they are not able to work outside of the home. One of my "students" is a cancer patient. Several are victims of hurricane Katrina and lost everything. This is my chance to help others.
Kids need their parents, but you need a life too. Only you know how much time and energy you need and can give to a full time job and parenting. You also have to leave time for yourself. However, I have found that I need to work. It makes me feel productive and happy and more confident.
Remember, you will be no good to your children and family if you do not take care of yourself first.