Are you even aware that this can happen? Life with two kids keeps us moving a little faster, and things get missed. Did you manage or compensate or dismiss it as life with two (or 3 or 6...)?
We took plenty of at home pictures (although probably slightly less than of Baby #1), and had 'milestone' pro photos taken just as frequently as we had for Baby #1. That was intentional. Less intentional, and more circumstantial, are the new clothes-- there's not much of a size difference between my boys, so there's not much opportunity for handing-down. As for attention, they're so different that they demand attention in different ways, so it works for us. I don't *think* I treat them any differently. We'll see in 20 years when they're complaining about me ;)