[pomian]

From personal experience I think don't rush it and worry about it. Reading gets more fun - perhaps because it is more of an individual understanding - (you read alone and to yourself), after grade 4 even better - grade 5 and 6. I would suggest some 'classic' adventure stories: most books by Andre Norton - the time trader series for example; Jim kjergaard - Big Red, later on Zane Grey. Good luck. Have fun with those kids!

[octobus2021]

My 8yo partially dislikes Geronimo Stilton books because they're "too old" (they started in 2000s and are now mostly done publishing the new ones). The books you mentioned were from mid-20th century :)