It's weird but I still do a double take sometimes and go Oh yeah, the second kid's a boy (as opposed to the first kid). Because there's genuinely no difference in the day to day. The same constant need for cuddles, the same curiosity and exploration, the same intensity of new experiences, the same messes, chaos and pain in the bottom. Even nappy changing is essentially the same (but with the added tension of vertical passing!). He really is just a baby. Like she was just a baby. So much so that I forget they are (allegedly) supposed to be different.
What I do notice very acutely though is the difference in their base personalities, which completely and thoroughly suffuses everything they do, feel and perceive. Where she experienced and responded to everything with an explosive intensity, he does so with a gentle curiosity. And I relish in observing this contrast, fascinating stuff.