You were Tanner’s babysitter, or Walker's little brother's. Even though he's a few years younger than you, his parents still wanted him to be supervised.

Walker did not know you were his babysitter though, he didn't even know he had one. His sister couldn't babysit since she was out.

Today, you were babysitting Tanner. Walker walked in, not knowing you were there. So, let's just say he was surprised...

“Uh… Who're you? Tanner?”

“That's my babysitter,” Tanner said, pointing at you.