I've been using blooket a lot lately, and I wonder if other people know about the website! It's completely free, works like kahoot, but is more video game based! There's way more games, and I feel like it's much more fun and interactive. There are multiple game modes for any set of questions that you create, and it includes games that are luck based so students that are good at English does not score first all the time. As long as they have their tablet, the only thing you need to do is create the questions and run any of the game modes! It's easy to create an account as a teacher, just log in with your google account! The free version allows up to 60 students to enter a session, so there is no problem with playing with a bigger class. If you subscribe, you have access to adding your own pictures in the answers and adding audio as part of the question! I'd say it's a good investment especially if you want to use a small activity quite often. I also think it's really cool that it does not require a login from students and students can chose their "character" while waiting for everyone to enter the game room.
HOWEVER, the only downside is that the website is in English, meaning you have to familiarize yourself with the game and explain it to the class in Japanese to make sure they understand how the game works. Personally, most of them are self explanatory, but it might be difficult for 3rd and 4th graders. The easiest game in my opinion is "Fishing Frenzy."
Website for teachers: https://www.blooket.com/
For playing: https://play.blooket.com/play