G'day mate,
While for the youngsters this may be way too early, kids of the age 6+ would enjoy a story about creating toys out of nowhere.
I used the Tinkercad to demonstrate how we can draw a geometric shape (which they just happen to learn) and had it pre-printed to show the result.
And of course, do not forget the giveaways!
You can find quite a few ideas on the Thingiverse. My experience is with the Cuddling cats - you can find my feline army there, and I lately print in different colors signs "I love Modiin", the later being my hometown. That proves to be the unbeatable hit.
Cheers!