This is the 17405th most frequent Turkish word.
üzerlerine
"Üzerlerine" means "on them" or "onto them" in English.
In this sentence, 'üzerlerine' refers to the leaves as the object upon which the children sat.
Çocuklar yere düşen yaprakları topladıktan sonra üzerlerine oturdu.
After collecting the fallen leaves from the ground, the children sat on them.
Here, 'üzerlerine' indicates the location on the birds where the snowflakes landed.
Kuşlar, üzerlerine konan kar taneleriyle beyaza büründü.
The birds were covered in white with the snowflakes that landed on them.
In this context, 'üzerlerine' describes the books as the surface where names were written.