We forget and for many of us we do not either feel love or our love has matured. Less hormones equals less passion, right? Also, the culture has changed from when we were dating. So, avoid summary thought while writing our characters if it is just because we can't generate the entire thought process.
Try Brian Hyland's 1962 hit, Sealed With a Kiss on your babies. Will they get it? Do people still mope if separated when there is all this social media? Skype? I think a kiss carries the same impact, even if it is only to seal a letter. Obviously, it's emails etc. not letters. So do kids sign off with SWAK?
Kissing for any purpose needs practice.