One simple and fun science experiment that you can help the kids complete involves getting creative with flowers and colors. Buy a bunch of white flowers, such as lilies. Fill two glasses with tap water. Mix a pipette full of water-soluble food coloring into one of the glasses. Split one of the stems of the flower from the bottom along to the flower head, so there are now two main strands for a stem. Place one of the strands into the food coloring solution and the other into the regular water, and leave them overnight. Have the kids observe the lily the next day. Half will be the color of the food coloring that they chose, while the other half will remain white. This is because the flowers' capillaries carry the water up through the flowers.
An idea for a science experiment that your kids will love is causing a basic chemical reaction to make invisible ink. Pour a few inches of concentrated lemon juice into a ramekin, and have the kids take the nib of a brand-new fountain pen -- one that has not had any ink in it -- and submerge it in the lemon juice. Get kids to write their names on pieces of plain white paper, which should just faintly show what they have written. Make sure the pen continues to write by resubmerging it in the juice after each letter. Allow the page to dry before taking a light bulb and shining it closely onto the pages, which will reveal the kids' names or any other messages they chose to write. This is because of the acidity of the lemon juice, which weakens the fibers of the paper and turns it brown when it is heated.
Regarded as a classic in the field of physics and in the study of gravity, this experiment of Galileo's can be done with any items around the house that are of roughly the same size but of significantly different weight, and a step ladder. Supervise and help the children as they complete the experiment, in which two same-size objects, such as a tennis ball and a shotput, are dropped from the same height at the same time. Before conducting the experiment, ask the kids to predict the outcome. Make sure you have a clear area in which to complete your experiment, and lay out something padded so the shotput does not get damaged or do damage when it lands. This experiment helps demonstrate to the kids why, under certain conditions, two objects of different weights can fall with the same rate of acceleration.
An earth science experiment may get kids thinking about the melting polar ice caps and rising sea levels. Collect four identical plastic containers of tap water, and mark the water level with a marker pen. This indicates your starting level of water. Put the four containers in separate places with different temperatures, such as a refrigerator, a dark room, a windowsill with sunlight, and a greenhouse. Have the kids collect the four containers after three hours during a brightly sunlit day. Get them to measure the increase or decrease in water level and take temperature readings of the water with a thermometer. Challenge them to think about how increasing temperatures in the Earth's climate can contribute to melting polar ice caps and rising sea levels.