Searching for experiments with microbes I came across this germ experiment which I thought would be a great place to start!
I have made a simple instruction set with predictions and observations available as a free printable which you can download here!
The printable has full instructions as well as what is required
On day one all that you will need to do is make up the gelatin and sugar mixture and separate it into your sample containers. You then need to wait 24 hours (or until the gelatin is set) to collect samples which you will see in part/day 2