Buying as a gift an app I already have

My grandkids pay Minecraft Pocket Edition on my iPad when they're here. I thought I'd buy them their own copies on their iPad and iPod.

I went to:

https://www.apple.com/itunes/gifts/

Which said:

Send your nephew the latest combat adventure game. Or your best friend that album you have on repeat. Just find the music, movies, TV shows, apps, or games you want to give on the iTunes Store or App Store. From your computer, click the arrow next to the price and choose “Gift this.” Or from your iOS device, tap the share button at the top of the screen.* We’ll send an email letting your recipient know about it. With one click, your gift will start downloading to their device.

I went to my iTunes Store on my Mac's iTunes, which knows I have it downloaded. No price is listed because of that, and the down arrow doesn't have "give as a gift" available.

How do I get copies of that game to my grandsons?