Songs are used to introduce many educational topics, and mathematical subjects need be no different. There are many outlets for finding songs relating to math, including free songs about negative numbers from educationalrap.com and CDs for purchase through online retailers such as creativemathematics.com. As an alternative, devise your own negative number themed lyrics.
Using pictures to demonstrate real life examples of negative numbers on the number scale can be fun and engaging for children, and may help them understand and visualize the concept. One way which you might do this is to purchase a large piece of poster board and draw a line through the middle of the longest side. Draw a large tree on the poster board, orienting it so the upper part of the tree extends above the line, and roots extend below the line. Draw a number line oriented vertically beside the tree, with the ground representing a zero and the integers above the line being positive, and below the ground being negative.
You could also use stories to introduce negative numbers, and give children word problems to solve regarding negative numbers. Word problems can help children relate negative numbers to their everyday lives, build English skills, and help prepare them for the types of mathematical word problems they'll encounter in later grades and on standardized tests.
There are many online video games designed to help teach children negative numbers. Some of these include Mystery Picture (dositey.com), and Line Jumper (funbrain.com). These games allow children to play while practicing integer recognition, and practice basic skills relating to identifying and adding negative and positive numbers.