When my 3-year-old is in a good mood, she asks for a “true love kiss.” She first heard the phrase during a family viewing of Shrek, but it has since become her signal that she is craving affection.

There are so many parenting questions but one of the main ones is whether it’s okay to kiss your kids, especially on the lips. If you don’t have kids of your own or have a baby on the way, coming ...