6 years old
Live animals for a Care of Magical Creatures class activity.
Live animals: frogs, cats, rats, owls
Proper safe space to care for the animals
Have live Trevors (frogs), Crookshanks (cats), Scabbers (rats), and most especially Hedwigs (owls) at your own Magical Menagerie display.
Children adore live animals, and many parties and events have an owl that gets brought out for the guests to see.
Arrangements obviously must be made with owner/trainers. In many cities sometimes arrangements can be made with a local animal shelter (SPCA), pet store or even a zoo for the use of the animals for the event.
The potential care (and sometimes mess factor) is always a consideration when planning such an activity, but it usually is a big hit!
Maybe too, have fun question and answer sessions with guests, with one person acting like Hagrid, and how they would take care of a Hippogriff, etc. It's more of a roleplaying thing for a host or staff member, but the guests enjoy it.