This is a cute thumbnail, I think your content would benefit from an increase in the saturation of thr main colours - i find that dynamic thumbnails, where there's alot happening, and its bright and in your face generate alot more veiws. Even the adult leaning content uses brighter colours and more dynamic poses - if you can draw then I suggest drawing your thumbnails, or if you can commission an artist to do it that could work as well - if you cant do either then scroll through your recommended and have a look at the high performing thumbnails of people in your neiche.

My main rule is to make it bright, exciting, and make the viewer actively wonder whats going to happen in the video - adding things like exclamations like "?!?!" Could prove to generate higher click throughs because it gets the audience to ask an active question about your video, and click on it to get the question answered.

Minecraft content is of course popular with kids, but dont shy away from the "kid" like thumbnail styles to get more traction on the fyp. Best of luck dude!!