I was a SAHM, at 21 (and a bit), our first child being born in 1963, and the second in 1966, and I don't think I ever considered that I could or would, go back to work.
There were no nursery facilities, but maybe a playgroup run by the Church.
As they they became older, I did a bit of accounting work at home for pin money.
Then when they were 12 and 10, I found a part time job, close to home. I had only been there less than a year, when DS2, made his presence known. So, again I was a SAHM, until he was 12. I was with a group of mums that started up a playgroup/ nursery, that opened just in time for DS2 to attend for a couple of terms before he started infant school.
Luckily we managed financially and didn't need an income from me.
I found another P/T job, that soon became full time, and I loved it, and stayed until retirement 17 years ago.
Looking back, at the time I don't think I realised how lucky I was being able to be at home, especially as now, as Witzend says, young mums would prefer to stay at home.