You can get creative about the way you make the squares, but the most traditional would be from construction paper, scissors and tape or just use white printer paper and markers. You can also buy the foam puzzles that lay on the floor that already have the letters and number on them.
This is a twist on the traditional hopscotch for little ones learning their ABC's and 123's. First start by making squares or rectangles with letters and numbers on them. Then lay them out all over the floor. Have your child start at one end of the room and see if they can cross the room jumping from square to square. They must identify the letter or number they are going to jump to next. You can also call out the number or letter for them and tell them to find it and jump on it next. Your kids can also call our letters and numbers for you to jump on. This helps the younger kids to learn their letters and numbers, and gives everyone some indoor exercise. This activity can also be done with shapes, colors, animals, etc.