How can I download & install Google Chrome on my son's iPhone?

I want to download google chrome onto my son’s iPhone. It’s his bday present. He turns 12 on June 5. It’s says I can’t do it. This is ridiculous, I am his parent and want that app on his phone. I trust google search and applications any day over Microsoft or Apple. How can this be fixed. I spent a lot of money on the phone. Thank you.

[Re-Titled by Moderator]