what robo and perry said jen, keep it short, keep the ob hive covered, unless a very short intro on who you are, what you do, then unveil, and engage with discussion/questions.
with pre-school to 3rd grade? at this age it is about 'show and tell', the more ya yammer, you might lose them. they just want to see the bees, the queen, and your equipment.
How long? short....
What to take? hat and veil, two if you have them (let them try on), hive tool, smoker and show them how it works, kids love fires........ (don't start it up but show them) a queen clip, wax comb if you have it, box with frames in it... anything that will grab their visual attention/curiosity and want to know what it's for and how it works, kids like to see, touch, feel, tell them how bees live in a box.....etc...
Should I provide a honey snack? HONEY STICKS! FLAVORED!!! (different flavors) kids love these!
What is the most important thing to discuss with preschool kids, and 3rd graders? kids at this age are visual, they need the stimulation from visual to keep the attention, so how a queen mates is really not gonna flip their trigger or how honey bees pollinate or other types of topics that will fly right over their brains. perry had a great example with the fruit! keep it simple, engage and encourage questions.
Where do I get a large poster, educational, to show the queen, drones, and workers? i don't have large posters but do have two pdf files i have passed out. not sure this will work for this age group.
EDIT AND ADD:
jen do you have an 8 x 10 color photograph of a queen with retinue?