It's common for players on minecraft to take turns placing signs next to each other if they want to have a 'private' conversation with another player (which is handy in some competitive game modes), and I've also seen muted players name their pets in-game with messages that they want to communicate.
The kids are doing a lot of impressive stuff. When building together, the owner of the plot leads other builders by literally showing them what and how to build, it’s way quicker than chat, they are very disciplined, repeat the building steps, then stop and watch the owner in order to see if they did it right. Sometimes they need a few iterations but it’s still quicker than chat.
