A Liquid Sandwich
You will need: Water, ink, salad oil, glycerin, and small bottle with cork.
Pour a little oil and an equal amount of water into a small bottle. Cork the bottle well and then shake it vigorously. The water and oil will appear to mix, but when you set the bottle down you will see them separate from each other. Soon the oil will be floating on top of the water. No matter how hard you shake the bottle you will never be able to make the two combine.
Sailors sometimes pour heavy oil on the sea to calm the surface for rescue work.
Try the effect of mixing other fluids. Use ink to distinguish between them if they are of similar color. With care and experiment, it is possible to fill a bottle with layers of different colored fluids, allowing heavy liquids, such as glycerin, to have first entry into the bottle.
Before children can understand a thing, they need experience: seeing, touching, hearing, tasting, smelling; choosing, arranging, putting things together, taking things apart. Experimenting with real things.
Old-time school teaching used only words and the teachers thought children knew something if they could repeat it. Now we know better. To reach practical understanding we do not need to use many words with young children.
Children are clever. They learn a lot, without being taught. The greatest skill - to be able to talk, to communicate is learnt outside school. In the classroom it's the children who need to talk the most. Unfortunately it is the teacher who does most of the talking!