Wait doesn’t wait on multiple objects. It just check the process table to see if any children have exited. If they haven’t it waits for a signal... any signal! It also sets a handler for sigchild. Unix in general can’t do the same for and arbitrary object because a) it requires that the waitable only signal a single thing, and b) there are only a small number of signals! So wait is a little special. Generally wait on multiple objects requires a general system to handle asynchronous ipc, which Unix doesn’t have (unlike say windows).

Also if you want to wait on multiple events, use a semaphore!