This is the 13780th most frequent Turkish word.
kıyafetlerini
"His/her/their clothes."
Here, 'kıyafetlerini' refers to the clothes that belong to Ahmet, indicating possession (third person singular possessive 'his clothes').
Ahmet kıyafetlerini değiştirmek için odasına gitti.
Ahmet went to his room to change his clothes.
In this context, 'kıyafetlerini' indicates possession of the clothes by the children (third person plural possessive 'their clothes').
Çocuklar kıyafetlerini bahçeye bıraktılar.
The children left their clothes in the garden.
The term 'kıyafetlerini' here refers to Serkan's clothes, showing possession in the singular form (third person singular possessive 'his clothes').