There are so many fun things going on when you make sun tea! I am afraid I went a little over board in my live presentation to my own preschool scientists, so hopefully I at least encouraged some curiosity We have plenty of sunlight these days, so I will give it another try soon.
The major observation to make is that, over time, the two substances in the jar became more like each other. The water took on the the color, flavor, and smell of the tea (diffusion). The tea bags became progressively more wet (osmosis). This is a demonstration of the natural tendency toward equilibrium. Equilibrium is the state were two objects have become enough like each other that they no longer influence one another toward sameness. Nature's tendency to bring everything to sameness is often referred to as entropy. Uniformity throughout the cosmos would be the ultimate disorder.
Was energy added or subtracted? It was added. Normally the energy is added through heat when making tea. In the case of sun tea, the energy is supplied as radiation from the sun. The processes of entropy, diffusion and osmosis, were enhanced by the addition of energy.
Speaking of the sun, look at that fascinating little pattern! We had a great time waving our hands around the jar trying to change the pattern, a hands-on introduction to wave- particle duality. I did not try to explain it to my pre-schoolers, though I am looking forward to that conversation one of these days.