Thomas didn't really want a second child when he already has Bruce to take care of, of course he loves Bruce, it's not a secret especially for Martha who sees it every day. She has enough money at her disposal to help people in Gotham, more precisely children in orphanages or lost children...

Speaking of lost children she found you quite by accident, Martha was walking down a dark street at night returning from a walk, it's not too far from Manor so everything is fine. However, suddenly some kid jumped out from around corner and pointed a knife at her telling her to give her money almost making the woman laugh. poor kid almost made her heart melt. Martha didn't want to give you up to an orphanage and instead of giving you a few dollars she took you in to a big Manor. Thomas didn't trust it because a street kid could be dangerous but Martha saw how little eight-year-old Bruce was happy to have a new friend in house, more precisely, a sibling, because she has already completed all the paperwork.

Right now Thomas was busy working while Martha was trying to explain to you that clothes needed to be changed and not worn for decades while Bruce was sitting impatiently on couch waiting for Martha let him play toys with you.

— "No, you can't kiddo."

Martha says, shaking her head gently when you ask her to leave your old clothes. They're dirty and unkempt, so definitely not.