You need to think about what is important to you and your family. YOU are important to your family, especially your children.
Do you need to work? If you can survive without the income, then I feel you should stop working, spend quality time with your children during their pre-school years, and concentrate on having a great family life, including extended family such as supporting your birth mother.
If you continue to be unable to go to work due to trouble with childcare... will work sack you? Would it be better to resign? At least if you resign, you can hope for a good reference. You don't say what work you do, but if it is something you need to keep updated with, are there courses that you can do on occasions, to keep updated with latest developments? Could you do any freelance work at home, perhaps for the company you currently work for? Or is the job not really something you are interested in anymore... time to give it up and go on to pastures new.
I worked for a company for 6 years and was made redundant. I thought the world had ended, but it haden't. I am now far less stressed than I was in that job and I am enjoing what I do now. Sure I don't get paid as much, I have few job prospects, but I like the work, I like the hours, I don't get overly stressed, and I manage to pay my bills. You need to aim for a balance in your life between work and family - I'm still not very good at that, do far too much work - but if I had children of my own, I am sure that would be different. Only you can decide what it is that you want to do.
If you resign your job, you no longer have a requirement for a nanny, so can make your nanny redundant. I believe your current nanny has worked for less than a year, so you can make redundant and pay notice period. Then forget it ever happened!
Life is too short to worry about things... live life to the full, spend quality time with your family.