One way to do this is to pay for a QR code scanner. There are several good free scanners, but they include ads. If you invest in a scanner like the Scan app, which is $1.99, your kids can use it ad-free.
If you are directing your students to a video on YouTube, whether it be a song, a reading of a story, or a short video clip, you can copy the link to the YouTube video and paste it into SafeShare.TV. You will then create your QR code using the SafeShare.TV link that you generated. This will enable your students to view only the video you want them to watch, without ads, and without additional videos. Yay!