4 grade science experiment need not be too involved and they can usually be one, with minimal help from teachers or parents. Children of this age are very curious and full of energy so they should have no trouble coming up with material to experiment.
One simple science experiment they might try to see if draining water always spirals in the same direction. This is interesting and easy to test. It also includes a little leg work, the kids will probably enjoy. All you really need to do is flush the toilet and see which way it drains, then fill the sink and see which way it drains, and then compare the results.
Another fun one could be to see what materials would protect the egg from six or eight foot drop. Some materials that you can use would pillows, bubble wrap, carpet. Styrofoam chips, towels and more. It’s pretty easy, just be sure to drop an egg from the same height each time and record your results.
One idea for 4th grade science project might be to see if the shape of an ice cube affect how long it takes to melt. You can test this by getting some ice cube trays in different sizes. These types of banks are usually sold at the Dollar Store. Then freeze the water in the body. Once they are frozen you can take even ice cubes each shape and place it on a dry surface at the same time and see which ones melt rapidly.