If you're looking for math activities to help your kids get to grips with calculating square inches and areas, start simple and keep it fun. All you really need is some graph paper, but if you want to involve your child's imagination and get them involved, you might also find a transparent film, the kind used on overhead projectors, with an inch square grid and rulers along the edges also comes in handy.
Getting to grips with square inches
The concept of square inches and surface area is a visual one, so first explain that one square inch is the space inside a square with sides of one inch, and draw and shade in one square inch. Once your child understands that, move on to squares and rectangles with longer sides, and explain how the area inside the box is the length times the height. Prove this by counting the squares inside the shapes, but be careful to start with small numbers your child is familiar with the multiplication for, such as a rectangle two inches by three inches, or six square inches.
Keeping it fun
Many children will quickly lose interest if all they are doing is drawing squares and rectangles and counting the squares in them, even if they do get to color the boxes in. You can counteract this for a while by drawing shapes that create a picture. Another way to keep calculating areas fun is to arm your child with a "square inch ruler," an overhead transparency or other similar type of clear film marked out with an inch square grid and rulers along the sides. They can use this to calculate the surface area of real objects, which makes it easier to make a game of it, and also shows a real world application of the knowledge they are gaining.
Give your child a square inch ruler, and a list of flat objects such as books, coasters and envelopes, and square inch totals, and have them match up each item to it's correct area to begin with. They can do this with books either by laying the guide over the book and counting the squares, or by placing the book over the guide and multiplying the height and width on the ruler. Challenge them to switch from square counting to multiplying over time to improve multiplication skills.
Moving beyond whole squares
Once your child has grasped the basic idea of square inches, it can take a leap of imagination to see how a circle, triangle or irregular shape can have a surface area measured in square inches. One way to help them make this leap is simply to draw a square whose sides are one and one half inches long. Show them that the two halves make up a second square inch, and that there is one quarter of a square enclosed as well, so the square has sides of one and a half inches, and a surface area of two and one quarter inches. Then move on to triangles, counting the bits of squares that make one whole, before moving on to circles and irregular shapes.
When calculating surface areas on paper loses it's interest, move the challenge into the real world. Go on a nature trail and challenge your child to find the leaf with the largest surface area, or to guess the square inches of random objects. Before you know it' they'll be better at guessing than you.