This is the 534th most frequent Lithuanian word.
vaikas
Child.
Here, 'vaikas' is used to indicate one's offspring or child.
Mano vaikas mėgsta skaityti knygas.
My child likes to read books.
'Vaikai' is the plural form of 'vaikas,' used to describe a group of children.
Vaikai žaidžia kieme.
The children are playing in the yard.
In this context, 'vaikas' is used figuratively to describe someone behaving childishly.