If you don't yell at your kids, how do they know you are serious? Specifically, children under the age of 4, who may...
It is not necessary to yell at your children, even those under the age of four. When you yell you are obiviously getting emotionally upset. Children are constantly trying to find the boundaries of what they can and can't do. As parents we must let them know the boundaries and that there are consequences for going over the boundaries.
Children are very good at pushing our buttons. They know what makes us lose our cool.
A better method than yelling is to set some rules, clearly communicate the rules and then let the child suffer the consequences of breaking the rules. For example if the child refuses to eat lunch, instead of yelling, tell the child, lunch is over in 5 minutes. You can eat now or you can wait until dinner. At the end of five minutes, remove the food. No big I warned you. Just remove the food. If you feel you must say something, say something like, "I bet you will be ready for dinner. It will be in about six hours."
Another example, the child will not pick up his toys. You can give him a choice. You can pick up your toys in five minutes or I will put them away for you. If I have to put them away, you will not get them back for two days. Then put them away in a room where he cannot get to them. You must stick to your word. Again, no I told you so. If anything, say something like, "It is really sad, you won't get to play with those toys for two whole days. I am sure you won't miss them." Do not be sarcastic. Be empathic.
If the child is not playing nice with a playmate again, tell him he either has to play nice or you are giving him a time out. The very next thing he does that is not nice, scoop him up and take him to his room. Again, let him understand that there are consequences to his action. While you might have to go through this exercise a few times for him to get it, he will soon and the next time you give him a choice, he will learn to take the choice that makes the most sense for him. He will soon learn it is better to eat his lunch than to go hungry. He must understand that the rules matter and breaking them has consequences. Your part is to stick to the rules. Do not be wishy-washy. The rules will not mean anything unless you enforce them. Remember, give him a choice just make sure you are okay with whatever he chooses.