The 爹、娘、爷、大、爸、妈 stuff fascinates me as well. Different environment calls for different characters. My take is that it has a lot to do with the class status thingy after liberation: the 非农业户口 (non-agricultural) class and 农业户口(agricultural) class.
Kids growing up as 农业 villagers in the 70’s, at least in my region, I suspect nationally as well, don’t call their parents 爸 and 妈. Instead, they call them whatever parents were called before the Liberation, or even before the first Republic was established in 1911, I suspect. Kids growing up 非农业, commonly viewed as being borne with a silver spoon in their mouths, almost always call their parents 爸 and 妈. In fact, any 农业 children who made a 爸妈 attempt were immediately suspected as “acting white“. In my local dialect, we call them 装洋 or 装洋哄(not sure if the last character is right, or even if there is a character for it).
I’ve always called my parents 大 (first tone. 爷 is also common) and 娘 (kinda between first tone and second tone, mostly first). Husband calls his wife 孩娘. Wife calls hubby 孩爷. I’ve noticed that children born in the 80’s and after, agricultural or not, use 爸妈.
I really want to find out the source of 爸 and 妈. Could they be new characters invented/introduced after the 新文化运动? Or they have always been there but I just don’t know due to my ignorance? I have never seen 爸妈 in what meager amount of 古文 that I’ve read. I looked for a copy of 《说文解字》while in Beijing in August, but didn’t find it in the bookstore I visited. Maybe I should have looked for 《康熙字典》instead.
Above is a slightly edited comment I left at Chris’ backup blog.