Think of it this way. You probably say Kevin's name 20, even 50 times a day. How does he know which instance of you saying his name you want him to come to you, atm he just has to guess. That's why you need to teach him a word that means 'come to me'.
When you teach come, do it in a place with low distractions, maybe inside the house to begin with, when you move it outside, like Ann said, it's best done with a lead on. Keep it close to start with as you are just focusing on teaching him the command, worrying about a distance recall comes later. To get a really solid recall into adulthood always reward when he comes. When they're young you should keep your pockets full of treats to reward him whenever he does the right thing.
Some additional tips for recall.
- Coming to you should always be a fun thing at this stage, puppies respond much better this way. Never make it a chore. So if you want to call him inside, which he may not want, when he first comes to you make a big deal of it, reward him, then take him inside.
- Your voice should be high and upbeat and you should adopt an 'open' position. An open position is something like arms held out (in obedience we teach people to hold their hands in the air so it can be seen at a distance), or a slight bow at the waist (mimicking a play bow). Dogs are much more responsive to these gestures and a high voice.
- Never ask them to come if they are distracted, always set a pup up for success. You don't want the recall word to become white noise. If you think it's going to be hard to get him to come to you then you should go to him.
Puppies, and adolescents, have a very short attention span, and recalls can be a challenge. I can tell you the no. 1 thing people go to obedience classes for is recall (followed by better control over greetings). Unless you're fun why would they want to go to you?
In more difficult situations there are a couple of good ways getting their attention and a recall. One is to run away - few dogs, esp herding breeds, can resist their owner running away. My Deska comes galloping if he even hears me say "I'm running away" just in case I am. The other is a squeaky toy. That squeak noise gets through that brain like a whistle. In my classes I have owners with highly distracted dogs, or pups, work with a squeaky toy. Doesn't need to be their favourite, just something that squeaks. A squeak toy that fits in your pocket is handy for taking on walks. And while you are still teaching him to come then a squeaky toy may fill the void to get him inside.