It seems to me that shapes are the most easiest for children to learn. Most will come to school already with the knowledge of the circle, triangle, square, rectangle, diamond, star and heart. Other shapes to teach are the trapezium and hexagon (shapes in the pattern blocks), and the oval and semi circle.
In the picture above, children are playing with the pattern blocks to familiarise themselves with the shapes. Always ask children to find shapes in their surroundings. For example, ask children to find things that are circles in the room. Looking at the above picture already they can see the paper plates (that we made into fish) and the containers. There is also a clock in the room and door knobs. This activity will help children to look for shapes in everyday items.
What I like about it also is that it will help children to draw pictures. For example, ask children to look at a house and ask them what shapes they can see (squares, rectangles and triangles) then show them how to draw a house using those shapes.
Drawing shapes is much harder for children although the circle is the easiest to draw. They will tend to have difficulties drawing the triangle, square and rectangle. With the triangle, show them how by saying the way to draw a triangle is to go up the mountain then down the mountain then back to the start. Give them plenty of practice with these harder shapes.
Children will also need to recognise the many different forms of the triangle. At this stage, they need not know the names but they need to recognise the different orientations of the triangle such as the isosceles, scalene, right angle and equilateral triangles. Tell them that as long as there are 3 sides, it is a triangle. (Don't forget that the rectangle can be laying down flat or standing up or leaning - they're still rectangles!)
Below are a few other examples of activities with shapes: