If something is left in your possession for more than two months, does it become your property?

i babysat twins and a six year old for two days and never got paid. when they came to get the children they left the stroller at my house. they didn't come get it, and it stayed on my property for over two months. i sold the stroller for fifteen dollars. the people i babysat for came to my house and told me i owed them for the stroller. was i legally in the wrong?