Youtube video saved to mini iPad/Asus Padphone

Hi, hope anyone can help me.
I have been searching good tool to save the Youtube view to my kid mini iPad and Asus Padphone. At home it is okay cause got wifi but when we are outside, it doesn't have mobile network. I want to download and save it to the iPad/Padphone so no need to view the same kid video in the youtube every time.

macworld.co.uk/how-to/ipad/how-download-youtube-videos-your-ipad-so-you-can-watch-them-offline-3441965/

Thanks Gary, is there also app for android?

Anyone can help please?