This is the 17903rd most frequent Polish word.
ławkami
"Ławkami" means "benches" in the instrumental plural form in Polish.
Here, 'ławkami' is instrumental plural of 'ławka', indicating 'with benches' or 'by benches', used to describe the relation/location of children in the sentence.
Dzieci siedziały przy ławkami w parku.
The children were sitting by the benches in the park.
In this context, 'ławkami' is also instrumental plural of 'ławka', signaling 'with benches' as tools or instruments involved in the action.
Uczniowie pomagali dekorować klasy ławkami.
The students helped decorate the classrooms with benches.
Here, 'ławkami' again is instrumental plural of 'ławka', representing the spatial relation 'among benches'.