As I understand it, these commands do not exhibit a parent/child relationship. They are both child processes of the shell that launches them. They would be siblings, in that sense. The shell arranges the standard input and output file descriptors of each process, such that the standard output stream from ls is the standard input stream of wc. Pipes between processes does not imply a parent/child relationship, although such may be the case, where a process itself launches a child process, and arranges the same sort of standard IO arrangement as does the shell in your example.
This sounds like a question to settle a bet, no?