Agars, oh how I've missed you... My university days were filled with sterlizing the tips of metal loops over a bunsen burner and swabbing blood agar with bacteria to grow. Funny story - for Valentines Day I gave the boy I was dating a blood red agar with an outline of my lips. It actually worked! I kissed the agar and incubated it and after a few days...there those bacteria lips were! Complete with a sharpie written note on the agar lid: "Just want you to know what you're kissing...Happy Valentines Day!" Side note: He never did ask me to marry him.
Make boullion gelatin agar cups for the bacteria to grow on: Place 1 cup cold water in a mixing bowl and sprinkle 4 envelopes of unflavored gelatin powder over the water. Let it sit for 1 minute. Pour in 3 cups hot water and stir with a spoon until the gelatin completely dissolves, about 5 minutes. Stir in 3 Tb bouillon. Pour ¼ cup of gelatin liquid into a short clear cup. Repeat 14 times so you have 15 clear cups filled with gelatin. Cover each cup with plastic wrap to keep out bacteria. Place the cups in the refrigerator for 3 hours.Sit the plastic cups on the counter for a while, with the plastic wrap still on top, so the gelatin comes to room temperature before you use the agars.
You can make up a batch of agars and then test to see what types of things prevent bacterial growth the best. Swab separate agars with hand sanitizer, vinegar, lysol, bleach, or whatever else you can think of that might prevent bacteria from growing.
Have your child use a Q tip to dip in a household substance. Swab it across the firm gelatin in a “Z” shape down, then rotate the cup 90 degrees and swab from top to bottom across the length of the cup back and forth until the whole surface is swabbed. Label the agar cup with a sharpie so you know what substance you used and let the agar sit out on the counter for a few days.
Have your child record her observations each day. What substances keep the bacteria away the longest? Moms, be sure that when you see bacteria start to grow that you just chuck the agars. We don't want any little ones getting into the bacteria or otherwise effected.