I can't believe I even have to say this. Don't hit your kids.
1. They are smaller than you but they won't ALWAYS be smaller than you and all you've done is taught your child that smacking someone weaker than themselves is OK. That won't sound like such a great idea when your baby boy or girl is towering over you by about 6 inches and outweighs you by 30 pounds.
2. How would you like it if your boss came up and whacked you every time you added up a column of numbers wrong or if you were late to work by 1 minute? It's not nice.
3. If you don't want to raise violent children, then don't model violence in the home. They do what they see and this can make them mighty unpopular with the administrators at school later on. Save yourself the trouble now and stop raising violent kids.
4. It may be tempting to give the kid a quick push, shove, whack, etc. but act your age! You are supposed to be in control of your own temper by the time you are old enough to have kids.
5. It doesn't work. No, really. It doesn't work. Yeah, yeah. I've heard it over and over, "My parents spanked/hit me and I turned out OK." No, you turned out to be a person who would hit little kids. That's NOT OK. Jeeze, do you think it's OK to kick puppies too? I had a father who was a proponent of corporal punishment and all it did was teach me that he was an asshole.
6. There really are better ways of dealing with kids who are acting up. If they are too small to reason with then STOP TRYING TO REASON WITH THEM. Simply remove them from the situation. I've found that a firm hold on the child along with a soft "Shhhhhh" repeated into his/her ear can really help.
7. Whispering is more effective than shouting. I am serious. Try it.
8. If the child is old enough to talk then time-outs can be very useful. Again, it's removal from the situation that's causing a problem.
9. As they get older yet, you have to find out what they value most and then take it away from them. Cell phone? Gone. Video games? Gone. TV? Gone. Yes, it's OK to take their bedroom door off the hinges to prevent door slamming tantrums. No good behavior, no door, no privacy. You'll be surprised how fast that works.
10. HUMOR!!!!!! More bad behavior can be derailed by humor than any smack down. As soon as they understand English the old "I'll bet you can't keep from smiling" trick works almost every time! Do something stupid, make a dumb joke. Sometimes it will just piss them off more but very often it will break the tension.
11. Misdirection. OK, we all know this one. Change the subject, give the child a different toy, move to another location.
And then, there are times when you just have to wait it out and here's where you have to become the adult. Do not give in to the temptation to lash out either physically or verbally. This is a test of your character and you don't want to fail because your children are watching - you want them to develop character so show them how it's done.