I'm not blind (my son is legally blind and going totally blind and I find this sub helpful in finding resource for him) but I'll share a few thoughts since we commonly get questions from other children about blindness because my son (only 7) uses a white cane.

I would suggest explaining how if you see someone with a guide dog, that no matter how much you may love dogs, you should never touch it because the dog is working to help make sure the person it's helping gets to where he or she is going safely.

If you do want to talk about a white cane, I would explain what that does, too.

I also find children that age (I was a Girl Scout Brownie, too) are fascinated when they learn about Braille and the fact blind people can read with their fingers. They usually find it really cool!

Have fun at your event!

Note: please excuse any typos. I recently had some brain procedures and am noticing typos as a side effect

Etiquette is a big thing. I'm glad you're covering it. If you just spent all your time on just that, it would be a really big deal but you're going the extra mile and I commend you for that. The obstacle course is a great idea. The more familiarity you can create, the more likely the lessons on etiquette will be absorbed. You're creating a group of ambassadors right there.

You may also be the only one to mention the fact that some service dogs are trained to get help for their human and that if they see a service dog alone, they should find adults to follow the dog and provide any needed assistance. I'm not down with sending children after lone service animals but they can def alert a grup. Scouts are the perfect problem solvers for such a situation as safety is already a big part of their training.

(former leader, here.)

Realize that this is an opportunity to educate both the little ones, and the parent of the little ones as well.

Have that play into your design of your presentation.

I really like the idea of an obstacle course to show how a dog died human relationship works.