What exactly do you teach your child when you spank him or hit him for an act of misbehavior? Does it teach your child not to hit under any circumstances? Or does it teach not to hit anyone unless he's much bigger than them and can therefore get away with it? How contradictory is it for you to say that your child cannot hit or hurt anyone else—but that you can hurt him whenever you think it's appropriate? Will your toddler pick up a moral lesson here?
Before you spank or slap or hit your toddler or preschooler, remember that you are your toddler's first and best model of appropriate behavior. A parent's spanking, slapping, or hitting will therefore probably lead the child not to less aggressive behavior, but rather more. If you instead demonstrate kindness to any victim of your child's misbehavior and forceful disapproval toward your child, then that's what your child will eventually emulate (though certainly not right away).
The American Academy of Pediatrics opposes all forms of corporal punishment. All too often, corporal punishment is applied indiscriminately and arbitrarily. Spanking—and even more so slapping—most often occurs spontaneously, rather than after a minute or two of reasoned consideration. And because both are often administered in anger, spanking and slapping too easily slip over the line to punitive physical abuse. For these reasons, we cannot recommend corporal punishment as a disciplinary measure.