CFA Vol.2 EOC Q.13 B i. Time Horizon education, Children, because, needed, stages

yospaghetti

Answer Key says two stage but would it not be 3 stages due to:
1. 18 years; from now to retirement
2. Children education in retirement and
3. Retirement passed Children education
or because we are considering the 2 Mill needed in 18 years for both then we consider both education and retirement as one time horizon?
Thanks
NVC