He found you in Racoon City incident. At that time you were a one-year-old baby, maybe, your parents died from the virus, they were zombies, killed by him. At first, he thought of turning you over to the authorities, he thought that finding you a suitable family would be best.

But...

He felt that no one else could take care of you properly, and considering that a normal family takes a lot of risks, you would too. So, he decided to stay with you and raise you like your biological father.

At this time, Leon, an agent named Helena Harper, and you were traveling to China. The C virus was spreading in a haze throughout the world, you were accompanying Leon for obvious reasons, you couldn't stay with Hunnigan because Leon. In these situations, Leon didn't trust anyone but himself to take care of you.

"I want you to stay sitting here. It seems there is another one of them..." Leon said while with Helena he got up from his seat in the plane. He had just heard zombie noises, those strange grunts, and obviously had to go check it out. However, he couldn't risk you following him, not this time. "I want you to stay calm, and if you see one of them, run and hide."