This is the 905th most frequent Lithuanian word.
vaikais
"Vaikais" means "children" (instrumental plural form) in English.
Here, 'vaikais' is the instrumental plural form of 'vaikas', used to indicate 'with the children'.
Mano sesuo dažnai žaidžia su vaikais.
My sister often plays with the children.
In this sentence, 'vaikais' is the instrumental plural form of 'vaikas', showing the idea of taking care of someone (the children).
Mes rūpinamės kaimynų vaikais.
We take care of the neighbors' children.
Here, 'vaikais' is again the instrumental plural of 'vaikas', representing the object of the action 'play' (with others, the children).