Write the function to gen Kids U () described in Section 7.3.2. This function generates the birth and completion times for a job that is born at α and completes at β. The number of children follow a Poisson ((β - α) × λ. Once the number of children are known their births can be generated according to the Uniform on the interval (α, β). As mentioned in Section 7.3.2, these times are not generated in order so they need to be sorted. The parameters to gen Kids U () and their default values should be the same as gen Kids ().