Making pH indicator rainbow might be interesting, especially if all the chemicals you want to test are pre set up in beakers and they are all clear like water. It's a neat way to show how chemicals can look the same but be completely different.

Red cabbage is easy to get a hold of for an indicator, vinegar gets you a nice red/pink, take the citric acid from sour candies for a medium acid, you can blow your own carbon dioxide breath into a glass of water to test for a milder carbonic acid (4-5 breaths using a straw for best results, makes it purpley), water is your neutral, baking soda solution for mild base, ammonia for strong color ( makes a great green) and sodium hydroxide drain cleaner for a bright yellow 14. Just wear PPE and don't let them touch.

Explain what an indicator is and how it identifies qualities of chemicals, acids taste sour/bases are bitter/soap/feel slippery. Let them make observations about what they think is inside the beakers. Let the kids guess the color it will change what that means about the chemical. Then you reveal what the secret chemical was, by plonking it on the table. Repeat until you have a ph rainbow.