This is so true. After having the kid... everything changes. Not immediately and not in every way, but, you become a mom and he becomes a dad, and those are so much more "roles" than just male and female. It's easier to be sort of equal and break through typical expectations when it's just the two of you, but a kid adds expectations, needs, a whole new set of perspectives, and some of the basic behaviors are just initially set a certain way.

Like, one of you is going to be more physically weakened by being pregnant, even if you were the athlete before this. One of you is going to be getting up more often to feed a kid, even if you switch to formula (which of course you mustn't do). And then once a kid starts responding to you in the park or the playground, you will be having a different kind of relationship, and a different set of options with other parents or school administrations, and structures start to seem harder to get around than they did when you were young and free. And maybe his good dad-ness shows up more as taking the kid out to play, joking around, and being better at discipline, while you focus more on teaching, talking about emotions, or setting up art projects, and suddenly you're both good parents but living stereotypes.. whether you're encouraged by advice and social norms or personal tendencies, if it happens at all you lean into your gender roles more than before.

You get more time off from work, more social allowance to depend on him after having a kid, while he becomes more openly recognized as a producer and a provider... Roles just get reinforced more regularly. It's so much easier to fall into them, and once a child goes to school...