Hitting?
I don't see much point in euphemisms in this case
Swatting, smacking, and spanking are all euphemisms for hitting.
I see three types of evidence for making a decision on this: science, folk wisdom, and personal experience. Science says that hitting is bad. Folk wisdom says that spanking, swatting, and smacking are necessary, but is mostly unable to recognize that these things are hitting, and that it's generally not cool to hit people who are smaller and weaker than you. Personal experience says that hitting kids is bad news.
My husband was never spanked. I was. He's never feared his parents. I did. My fear of displeasing my parents caused some pretty severe problems. Between me and my husband, he is *definitely* and by far the better adjusted.
In any case, I'm open to other opinions, but retreating into euphemism is a pretty sad approach.
Hit: 1. to deal a blow or stroke to
Swat: 1. to hit; slap; smack.
Smack: 1. to strike sharply, esp. with the open hand or a flat object
Spank: 1. to strike (a person, usually a child) with the open hand, a slipper, etc., esp. on the buttocks, as in punishment.