Its not really that hard to get this
1. Get yourself a Home (in Whiterun for example cost 5000g without anything)
2. Go to the person where you can upgrade your house and choose to make a children room.
3. Go to Honorhall Orphanage after completing "Innocence Lost" or look at the street to find a homeless kid.
4. Talk with the Boy/Girl and say in the conversation you want to adopt her or him.
5. Send him to your home and VOILA!!! you got your trophy.