A process is a child process if it's a process that was spawned by another process (anything other than the first process)

1. No, you don't need to call wait after spawn, but wait means the current process will wait for all of its children (if it has any) to exit
2. A process that waits is just waiting for its children to exit. If it doesn't have children when it calls wait, it gets moved to the ready queue. Once all its children exit, it gets moved to the ready queue as well.