If your question is how many positions are possible, then the answer is 24.
We find this by thinking of how many people can be in each spot. If there are 4 spots each person can stand (back left, back right, front left, front right), then there are 4 possible choice for the first spot (mom, dad, son, daughter), then 3 for the next spot (since 1 is already in a spot), then 2 options for the next spot, and then 1 option for the last spot. In other words, the answer is 4x3x2x1, or 4 factorial.