Another variation is to ask the child to draw. First make some sticks, circles, squares, or other shapes on a page, and encircle them. Make for the child a big "bubble" to draw in, and ask the child to draw either the same amount, one more, or one less. Also have your child practice writing numbers on paper.
In the simplest cases, the two fractions will already have a common denominator. In this case, add the numerators and then reduce the resulting fraction.