A peck on lips to small children is extremely common.
Does nobody in this thread have kids?
I love the "I wouldn't do it" comments. Seriously get over yourself.
As someone else said 1-7 is about the correct age.
When kids get into about 4th grade and start noticing the other sex is the right time.
Usually the kids let go at some point and let you know when to stop through actions or body language.
Boys stop sooner than girls.
Usually harder on the Moms.