It’s my understanding that you remain just as selfish/ selfless as always when you become a parent, it’s just that your selfishness/ selflessness now encompasses more people. If you used to always take the last biscuit- you still take it- you just give it to your child, rather than eating it yourself. You still don’t offer it to your sister.
I don’t know if that’s what the expression is supposed to mean but yes I think this is pretty much what happens in real life. The scope of selfishness just extends a wee bit .
My childhood friend (I say friend but I don’t really speak to her anymore) has always been selfish. She has been a massive taker from when I was younger to now and I fell into the role of giver.
When she had kids she always talked about how you can’t be selfish now when you’re a mum and speaks as if she’s so selfless but she’s not. It’s just different selfishness .
For example instead of being grabby about getting things from me solely for herself she now tries to get stuff from me for her kids too. She will talk about her problems endlessly to me and trigger my mental health but she will be a martyr at home to be a “selfless mother”.
She won’t reciprocate any of it as well , which is why I now feel drained emotionally and financially by her and the friendship has kind of died.
so to answer your question OP, no having kids doesn’t make you less selfish. And in many cases it makes people more inward looking . Same with marriage.
Look at all the ones MN with the mentality that no-one matters apart from their “little family”
Yes I get parents sacrifice certain things for their kids and put some needs on the backburner for the good of their children, but many also see their kids as an extension of them or at least as people who it’s in their direct interests to make happy and successful . It’s not as if they’re helping some random kid they’ll never meet in another town, city or country. Don’t get me wrong it’s important to look after your kids and you should do first before you help others but I’d hardly fall it selfless. It’s just living up to your responsibility that you signed up to as a parent.