Based on business scenario Parent and Child case dependency can get change..
Nowhere pega will tell always Parent case needs to be resolved after all child case got resolved like that..
Based on business need if you want you can resolve Parent Case after Child Case got resolved, if not you can resolve the parent case before all child case getting resolved also..
In above challenge they mentioned only creating child case. if Parent case needs to wait until child case resolves "then need to use wait shape after create case smart shape "
Wait Shape Configuration:
Select Wait type:- Case Dependency and select the child case for which needs to wait.