Finances after baby

Simply out of curiosity, as I’m not currently TTC, what is the typical way finances work for a sahm? My hope would be to stay at home as long as possible once I have children, and assuming I’ll be married by then, I’ve always been so curious how people structure their finances. My partner currently is not the ‘what’s mine is ours’ kinda guy regarding money, which is fine for now as I make my own money and I don’t expect him to support me, but once we have kids does that normally change? How much freedom is normal when you’re on one income. Like do you ask for permission to buy small things, like say you wanted a Starbucks or something similar.

I know this isn’t a direct question and I’m not trying to be intrusive so only share if you’re comfortable, I’m just really curious how it all works on a shared income, and also how much people save before becoming a SAHM. Thanks!!