If you're consistently miserable, you're right that this situation is untenable in the long term. However it sounds like quitting right now isn't going to work either.

Right now you're casting your husband in a position of opposition to you when you should be on the same team. The problems he's raising with you quitting are real problems you would have to face together, and the problem you have with hating your job is also a problem you should be tackling together.

Instead of saying 'I hate my job and want to quit and do retail', say 'I hate my job and we need a plan so that I'm not stuck in it forever'. Look at what your finances can handle and therefore what jobs you can apply for without fucking your bank balance. Look at the possibility of saving for a future career change. Look for cheap qualifications you can get to enhance your employability; some IT courses could allow you to apply for secretarial positions (I think you'd have a good shot at school admin given your childcare experience) or you could develop a specialty in children's respite or residential care.

If it's nannying specifically that's the problem, there are childcare related jobs in which you aren't always alone and bored. Do those need to be off the table? What needs to change for you to get one that appeals to you?

Basically, your husbands concerns are valid as is your need for a job you don't hate. You need to get on the same team to fix this in a way that works for both of you.