On the new TV show 'Supergirl', in the intro the protagonist claims that she was sent to protect her cousin, Superman. While the original plan is to have Kara protect Kal-El (Clark/Superman), however Kara's transportation got lost and Superman grew without her.
The thing is, why did Kara receive that mission? Both weren't adults at the time, so it doesn't make sense for neither having to take guard of each other. Only thing that could be explained would be them staying together and being raised as twins, which then would mean Kal-El would've received the same mission.
Why was Kara told to protect Kal-El?