Do Not allow Children to do this without complete adult supervision. Melt one color at a time. Mixing the colors when melting sometimes results in making strange or muddy colors. Place the chunks to be melted in a glass microwavable dish and heat on high for 10 seconds in the Microwave oven. If it is not completely melted, heat for an additional 10 seconds at a time until it is melted.
Different brands melt at different times.
Do not overheat. Do not leave the melting soap unattended. Heat only until the soap is melted. You can make plain bars or use the soaps that would not melt by cutting them up into thin chunks and pressing into the melted soap. This will make what we call chunky soaps.