Exponential growth is the type of growth when the population size or the rate of growth increases exponentially i.e., the growth rate increases with a greater speed. However, the per capital rate of growth remains constant. If the growth rate decreases with the increase in population size, then it is logistic growth.
If the couple have two children then it is logistic growth and more than 2 would lead to the exponential growth. The growth curve in exponential growth continue to increase whereas in logistic growth, the growth curve comes to a maximum level and maintains it.