Write some 2 and 3 digit numbers on some stickers. These will correspond to each other so that they are a double and a half (some numbers may overlap).
Children have to match pairs of stickers to find the doubles / halves. This is differentiated and involves movement and quick-thinking skills. Children can write the numbers as well. The activity can be extended so that children have to represent their number as a decimal fraction on a number line or a proper fraction in a drawing.