Adopted to be a Holmes

"A couple have been murdered. now, i need you two to come and investigate."

Sherlock and John arrived at the crime scene, and on the swing in the garden, sat a boy wrapped in a shock blanket. He, Wayne Ballard, is the son of the murdered couple.

"So... would you two live and take care of him for a while?" Lestrade asked after the two investigated and made some simple and primary deductions.

So that's how Wayne Ballard is now living with Sherlock Holmes and John Watson.