This is the 461st most frequent Ukrainian word.
дітьми
"Дітьми" means "by/with children" in English.
"Дітьми" is used here as an instrumental case plural of "діти" (children), indicating with whom the action is performed.
Вона грається з дітьми в парку.
She is playing with children in the park.
Here, "дітьми" remains in the instrumental plural form, describing the association or accompaniment of the mothers with their children.
У парку було багато мам з дітьми.
There were many mothers with children in the park.
"Дітьми" again is the instrumental plural form of "діти," showing the participants with whom the action of conducting the lesson took place.