Some fast-food places have Braille on the drink lids, next to those...things that you push in to mark what drink is what. But the restaurants that have it seem to change from country to country and state to state. More info $1. Many sit-down restaurant chains will also have Braille menus available; in the US, I've gotten them regularly at Ruby Tuesdays, in Canada Swiss Chalet usually has them. But any large corporate chain should have some; smaller individually owned places never ever do.

Perhaps talk about audio description? It's available on most Disney DVDs, and children's cartoons seem to be the things that have description most often. As a quick example, here's $1 audio described. It's an especially good example to use, because listening to it with your eyes closed, you couldn't get anything at all out of that without someone describing it.

Accessible computer games, played only with sound, are also a thing. Unfortunately, most of them are difficult enough that I don't think kids that age would enjoy them. BSC Games used to make a nice space invaders audio clone called Troopanum, but the company went under, and I don't know what happened to the games they developed. There is $1 that makes some easier games, but as I recall, some of the voiceovers in those games are...not exactly inappropriate...but PG-13, maybe.

Perhaps some of the kids in your group have heard audible traffic lights? That really depends on where you live, though. You can hear the audible lights at Toronto's Yonge and Dundas intersection in the background of $1 made by our own /u/drop9reddit. But there may well be some audible lights somewhere near you.

Blind people are also the reason subways and buses in Canada, the US, and the UK usually announce what stop they're at. On the off-chance your local bus doesn't do this, here's $1 that I made back when that feature was relatively new on the Toronto subways. Why did I record that for five minutes? And not say anything? Good grief!

I also made $1 printing out a page of Braille. It's more interesting...slightly.

In Europe Braille is used is even in medication packages, at least OTC, depends on country.
Plus on many other medicine type products.

In USA it's too rare to find Braille in products.
But room names and numbers in public buildings always have it. You can also find the elevator/lift floor numbers everywhere brailled (ground floor is usually star symbol or number 1)
Many L'Occitane cosmetic product bottles or packaging have braille - a lovely little details being able to read in the shower what I'm using (as if I couldn't tell from the scent).
Also some plant food bottles had braille; toxic for humans stuff but i so wish all tylenols, aspirins, cough medicines etc had the product name and dosage brailled on the box.

A few affordable ideas in US & Canada: you can get cheap children's braille books from seedlings (.org?), and a basic braille slate & stylus for writing for under $10 from braille bookstore online (free shipping for $10 or more, so maybe add a few silicone bracelets with braille alphabet to show and raffle).

Paths for Literacy might have a few cool ideas. :)

An alphabet map would be great to show too.

You can and probsbly should contact some local blind organization to see if someone could help show materials or how to read and write etc.
In many cities in US NFB (national federation for the blind) is great, but there is also AFB and ACB.
What city, state, or country are you located in? Maybe I can find some local ideas :)

Tactile pavong should be (in theory) around the crosswalks everywhere in IS. It's those squares with the lego like bumps, that are slanted to show which way the crosswalk is. Those are both for longcane and wheelchair users.

Depending on where you live some curb cuts are bright yellow and have tactile paving (the bumps). Some crossings also have audio, so it might say "cross, Bernard street" or it might just beep. There are actually two different beep sounds and they signal with direction is safe to cross, N-S or E-W. Elevator buttons also usually have Braille.

If you're looking for more examples of Braille, try an organization that provides services to people who are blind like NFBUK, Guide Dogs, Blind Children UK, etc.

Depending on where you are, usually there is braille in the wild and train stations, escalators, elevators, and even sometimes on Wall plates that designate what room is the bathroom or a specific room in the building. A fun way of showing braille might even be teaching them grade 1. You can use a cupcake tin with 6 cups and six tennis balls to go through the whole alphabet in a large and fun way.

Canadian paper currency has braille markers on it to help the note what kind of bills they are. Any street crossings with audible signals will usually have braille on them telling you what street you are about to cross. The more high-tech ones have buttons that vibrate to help tell you when to start crossing, and if you press and hold down the button it will even speak to you to tell you to wait to cross a particular street.

Some of the major hotel chains will add braille around door labels and elevators. You can also plan a trip to the library and find out about tactile graphics, braille books, and assistive technology.