We all did it when our kids were little, and many of our own parents probably did it for us when we were little. A young child falls, scrapes his or her knee, or maybe hurth their shoulder, or bumps their head, and the parent “kisses it better.”
Save for the bump on the head or sore shoulder, but an actual scraped knee, or some other sort of open wound, kissing it might actually help it heal faster. Saliva contains a “peptide” called histatin-1. That histatin-1 actually helps blood vessel growth, and is exactly why a wound in our mouth heals faster than one somewhere else on our body.
The actual saliva contains the chemical naturally, and they say that even the “tiniest bit may promote healing.” We’re not saying you should spit on your child’s wounds or anything like that, but it’s more of a “oh hey, that thing you do for children to help them “feel” better is actually more effective than you think” sort of thing. You know how animals lick their wounds? It’s a little bit like that, apparently.