The second baby is your reminder that these days don't last forever. That time isn't on your side. A reminder to slow down and enjoy the little things.
It's heartbreaking how quickly babies turn in to toddlers, then kids, then teenagers, isn't it? But with that second baby you know this. You remind yourself frequently to bury your face in those chubby arm rolls, kiss that fuzzy head, and just hold that baby for hours. Because it doesn't last forever. You blink, and it's over.