YANBU!
I haven't read through all the posts here so excuse me if I'm repeating anything.
I am in a very similar situation to yours and I think other people just don't get it.
I even understand what you are saying about option one; although I do think you should rule that out! It is so tempting to want to keep life the way it is.
I think it's appalling that this country does so little for stay at home mums, from the single ones on benefit to the ones in couples who can afford childcare. There is a stigma attached, as though you are lazy, when all you want to do is give your little ones the love and attention they need.
The reduction from 16 years to 7 years old is completely ridiculous as far as I'm concerned. Ok, so we don't need to be at home all the time while our kids are at school, but being there to drop them off and pick them up is a really valuable role (I'm not saying it's less so with a CM but I do think that there should be a choice.) Personally I think the reduction should have been 12 years old.
I think your thoughts about being a nursery teacher are really positive. Is your DD going to nursery in September? Maybe you could be a parent helper once a week to get some experience, and then do a course part time while she is at nursery? You could also look in to being a Teaching Assistant, the only problem with this is that the hours are pro rata (so that if you work 20 hours a week in term time, it averages at less than 16 hours a week over the year so you would still not be working enough according to the government! You would have to work 21 hours and 20 mins a week during term time for it to count as 16 hours a week overall.)
I have tried finding out about what the rules are on training when you are on income support but the staff at the jobcentre plus aren't that knowledgeable on that, they do try to help though and have been able to give me useful numbers (like the number for a training college). I think it depends what training you do.
I feel for you, especially when faced with the attitude that some people have. It's not easy on your own, it's not easy making these decisions on your own either.
And the "everyone has to do it" argument doesn't wash with me, everyone has to do a lot of things, doesn't make it right!
For me personally, I am going to start work when DS is 5, so that I don't have to worry how many hours I do, and I am going to do my very best to find a job that will start after I've dropped him off and finish before I pick him up. Ideally I will be a Teaching Assistant at his school, and then it wont be such a big deal if I take half an hour out to watch his school play etc.
Then I've got 2 years to gradually build up my hours so that I get the right life/work balance for me and my son.
Good luck to you x