Quoting P.S I'm pregnant ♥:" Do you allow your children ? Is it appropriate? Explain. *do age and gender play a factor ?"
I don't see it as an issue. We kiss my DD on the lips. In my culture, it's not inappropriate to kiss family on the mouth as a way to greet. So, at almost 30 years old, I still kiss my brother, sister, and parents hello/goodbye on the mouth. It's probably unusual to some people outside of our culture, but it's normal for us. Now that I live in the US,we still do that, and I don't think DD finds it odd. It's not like there's any sexual connotation or intention behind it.