My wife & I kiss both of our kids on the lips, son is almost 7, daughter is 3.5. Although my favorite spot to kiss them is their foreheads, because I like their unique scent that's there & I've been doing it since they were babies, at least 10 times a day each. But we're an affectionate family.
I know another guy who won't at all kiss his kids on the lips, never has even when they were babies, I've never actually seen him kiss his kids even on the cheeks or forehead, to be honest. But he's also the same type of guy who won't wear anything with pink on it and whose sons think wearing pink is "only for girls." Good guy, but he thinks like a neanderthal on these things.
Some people just like to make everything about a potential sexual appearance where there is none. And as a result I think it eventually cheapens, demeans, and furthers the taboo of sex with their kids.
I've seen this debated on social media and didn't think people actually saw this as an issue.
I grew up in a family where we did, and still do (for big occasions like ceremonies or someone going away on an overseas trip). I do it with my kids and don't even think twice about it. But it seems like people are making this out to be something a deviant would do.
The particular person I know who was making this out to be wrong is from an Italian background, so culturally I guess they are used to cheek kissing.
Throwing it out there...