First start by letting ur kid/kids make there hypothesis.
My daughter said they will sink.
Then place the pumpkins in the water and see if you are right or not.
Why do the pumpkins float? People have been wondering why things float or sink for
centuries. The Law of Buoyancy, called Archimedes’ Principle, states that a body floating in
a fluid is supported (or buoyed up) by a force equal to the weight of the fluid it displaces.
In simpler terms for this experiment, a pumpkin will float if it displaces as much water as it
weighs. When a pumpkin is immersed in water it experiences a force known as the buoyancy
force. This force is equal to the weight of the water displaced by the pumpkin.
Here is another example: A lump of steel will sink because it is unable to displace water that
equals its weight. But steel of the same weight, shaped as a bowl, will float. This is because
the weight gets distributed over a larger area and the steel in this form is able to displace
water equal to its weight.
As a result, a heavily laden ship floats because its total weight is exactly equal to the weight
of the water it displaces. It is this weight that exerts the buoyant force supporting the ship.
(Resources: A Moment of Science, Indiana Public Media;http://indianapublicmedia.org/
amomentofscience and Growing with Science;http://blog.growingwithscience.com/)