I was in a similar position. I was a temp from July 2006 until starting Mat leave in March 2007 before ds2 was born in April.
I was temping through an agency, so the agency had to pay my Mat Leave at the higher amount, and were obliged to look for work on my return, but obviously could not guarantee the hours I wanted.
I was very worried, thought I would never get another job, that I would end up taking any old job (nothing against any jobs, just that I really enjoyed the last one!) to pay the bills.
I went to see the Agency at the beginning of July as I wanted to return to work in September. They calle dme 2 weeks later with my perfect job! I know have a job I love, permanent, very well paid, hours I chose.
I never believed it would happen, but it fell in my lap! have more confidence in yourself, say sorry but no, and then start looking. It gives you a few months to find something perfect for you, if that happens before January then you might need to go back a bit early, but it'll be to a part time job where you are valued.
and my childcare is £750 for 2 children, part-time, and that's after the funded part is taken off, so not surprised by the full-time cost!