Albus had a sister called Ariana, who loved him dearly, but tragically, when Ariana was only ten years old and Albus was six, Ariana got brutally attacked but several muggle boys, and died from her injuries that same day. We don't know exactly what motivated the boys to attack her, or how they did it, or if they even got punished for it, best we think it was because they saw Ariana out in the streets and not at home, cleaning, because women and girls had little to no rights at all at the time.