Are you in the same location, or playing remotely?
If you're all in one place, you can use hotseat mode at a single computer.
If you're in different locations, your grandchildren can create accounts & you can create game tables and invite them to join.
Possibly useful for teaching: in the chat window (lower-right-ish) of an active game table, click to expand), in the lower right there's a pointing finger icon that lets other players see your cursor, so that you can point things out on the game board.
Wishing you many delightful games together!