An experiment is a procedure carried out to support, refute, or validate a hypothesis. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs when a particular factor is manipulated. scientific problem is something you don't understand but you can do an experiment to help you understand. Scientific problems are usually based on observation of scientific phenomena.
well, here are two ideas.. you can pick one you like.
First one - Skittles Science
A Lesson in: Stratification
A great way to get rid of extra candy, this easy science experiment for kids uses Skittles and whatever liquids you want to use. The idea is, the candy is made of ingredients that dissolve, so kids get a chance to guess which liquid will make the Skittles dissolve the fastest. Get more info over at Little Bins for Little Hands.
Messiness factor: 2 sponges
Second one - Pasta Rocket
Believe it or not, you can create a very simple hybrid rocket engine using nothing but some yeast, hydrogen peroxide, a jar, fire and ... a piece of uncooked pasta.
When you mix the yeast and hydrogen peroxide together, they react and create pure oxygen gas. When this gas is funneled through a piece of pasta, all you need is a little bit of fire and you've got yourself a pasta rocket.