I went back to being a SAHM when I had ds3. At that point I was working 25 hours a week as an Operating Theatre nurse (two long days and a half day), and it was costing me £100 to have ds1 and ds2 in nursery for those 2.5 days. My take home pay was £150, so when I became pregnant with ds3, it was obvious that my earnings would be completely wiped out by my nursery costs - basically I'd be working for nothing.
I was not enjoying my job - as a part-timer, I wasn't in line for promotion, and was overlooked whenever it came to providing any professional development that might have enabled me to apply for promotion, and I felt I got the shittiest work to do - the lists/surgeons no-one else wanted.
I was lucky that dh's wages were sufficient to support the family - my earnings had been extra - they provided some luxuries - so I was able to stop working and be a SAHM.
Shortly after this, ds1 started at school, and I think that, even if I had carried on working until then, I'd have had to give up at that point, because the before and after school club at their nursery would have been more expensive than a day in the nursery.
I was glad that I was able to be a SAHM - it worked well for the dses, and for dh and me - but I am very aware how lucky I was that we could afford to do this.
I do sometimes wonder, though, if I did the right thing. By the time the boys were old enough that I could have gone back to work, my registration had lapsed, so I'd have had to do a Back To Nursing course, and it would have been very difficult for me to get back into theatre nursing, which was the only area I had any experience in, as a qualified nurse. And by then I was too old (in my mind, at least) to retrain for anything else, so I did feel, to some extent, that I had no option but to carry on being a SAHM, and that there was nothing else I could do .