Hmmm... Looks like he is not too interested, maybe doesn't yet have his own reason to do it. By the way, look at these pages 👇, we have them also in Spanish. With others Bears and different motif as well 
https://www.bitcoin4youth.com/ellis-from-el-salvador-creative-pages-to-print-at-home-01/ Maybe he'll be interested in colouring, solving puzzles etc. Not directly learning English here but getting some words in between, once he gets interested it can get expanded with more /otter things. If he's too old for that, try a similar method - instead of making him learn English add for example once a week some activity that will make him use this language even just a bit. Maybe Sunday breakfast, whole family with a few words in English to be always exchanged, by everyone (naturally built habbit). Tuttle Twins move was a smart move 💜👏 Maybe add sth extra to it. But not to 'learn' English but do sth that will somehow include this language in it (Site note: I'm not trying to lecture you, just giving some inspiration ☺️).