Looking for the title of a book (big family, riddle, piece of paper)

Hi everyone

One of my students asked me if I know the title of a certain book she read back when she was a kid. It doesn't ring a bell at all, but I was hoping you guys could help me out. Here's her description:

"I have a vague idea of what it was about but i can't remember the name. It was a funny book and it has also been filmed. It's about a family, a very big one cuz there were loads of

Looking for the title of a book (big family, riddle, piece of paper)