You don't. In fact you shouldn't, and thankfully can't really.

You should love children (your own or others) like you hold a bird in your hand: If you try to make the bird stay you'll crush it, and it will either die, or rip its way out. If instead you hold your hand wide open and treat it gently, it will stay as long as it wants, and it will leave gratefully when it is time to go.

If you listen to, encourage, and mentor him, he will stay until it is time for him to move on. If you do that right, moving on will be a sad, but good time where he is grateful for all you've given him, and you are blessed from having known him, and feel pride in sending him out into the world.

If you try to grasp him, keep him with you, make that time never come, you will crush his spirit, stunt his growth, mess him up for life, and put yourself in jail when his parents come looking for the person who's trying to steal their boy. It will end like "True Boylover" and his boy in Dusk/Heather's web-novel: Messy and horrid and evil.

Be careful how you think about his presence in your life, and work with his parents and ask their guidance often, and always remember to hold him with an open hand.

Love in Christ,
~CSL