Since all the years of my career were spent with children , communication with children is extremely important. There's no one right or wrong way to talk to children...there are many ways. Each child is different as each adult is unique and so there will automatically be variations.
Basically all we have to do is focus attention on the child and make sure that we are speaking to the individual. We are talking to a human being so just because the person happens to be a child doesn't mean we have to change from our normal pattern of speech. Sometimes we see people using exaggerated baby talk to communicate with little kids . It may be cute and fun but the kid doesn't learn much when things are dumbed down.
One of my favorite short stories was about a boy who went to the store with his Dad to buy a pair of shoes. The clerk talked to the Dad and the Dad relayed the clerk's message to the kid. When the kid answered he spoke to his Dad and his Dad relayed the message to the clerk. It's a well told story and is a good illustration of what not to do. If anybody knows this story , tell me the author and a title as I can not remember them.
We don't have to over simplify our speech. Speak to the kid's level. Kids know when we're dumbing things down and we lose some credibility
Sometimes we have to catch a kid's attention. Most people yell and they do get the kid's attention but the yelling raises the stress level so, you have the kid's attention but have increased the stress. A stressed conversation usually doesn't go well. Patience helps. Take a deep breath. Lower your voice an octave. It usually catches their attention and doesn't cause any side effects.
Talking to kids is sometimes a challenge that increases our stress and things can get complicated in a hurry. I know. I've been there. I just know that if you can discipline yourself the conversation can be beneficial and fun. I like talking to kids on our street. It's always a pleasant part of my day and I usually learn something in a very interesting way.