A must do activity if you're going to Hoi An, is doing a lantern making class! Especially if it's a rainy day.
I did this workshop at "The Lantern Lady" and I honestly had the best time. I did this workshop with some girls I met in my hostel and there was another family with 2 young children sitting at our table. So this workshop is litterly for everyone!
The class itself took around 1 hour. You could choose what shape, what fabric, what color of tassle you wanted etc. And the lady helps you alot aswell if you need it.
AND it was only around 2 euros for this workshop!
Also if you're worried about the lantern taking up alot of space in your backpack/suitcase, they fold it up for you so it's as flat as possible.