What does 3D shape look like?
The Basic Idea
Ask children to make a 2D shape: Square, rectangle, triangle, pentagon etc and join the corners with the masking tape. What they have made is the footprint, one side, of a 3D shape. What can they tell you about it - facts. Encourage them to use Mathematical terminology.
Ask them now to make more shapes to turn their 2D shape into a 3D shape.
What can they tell you about it - facts. Encourage them to use Mathematical terminology.
If children are struggling to 'see' faces as you can see through the shapes, use tissue masking tape from edge to edge to help them count the faces.
How to take it even further or make it more challenging
You could take this further if you have time, by giving them tissue paper and PVA, and ask them to make coloured faces to their shapes. This helps reinforce the 3D nature.
Ask the to make 2D shapes and combine them in different ways to make 3D shapes. What can/can't you join? Why? Why is it challenges to join an edge of a triangle with that of a rectangle? What do you have to make sure in order to do this?
Alternatively, ask children to make lots of squares and rectangles and make a nett or a cuboid, or triangular pyramid, or square-based pyramid. Get them to demonstrate how it can be folded up to make 3D shape and unfolded to make a nett.