"The child drinks water."
Translation:Đứa trẻ uống nước.
Is "đứa" a classifier? This is an excellent question. I would say so, but đứa can only be used for children, or young people that are yet mature. Đứa is more of a description of those who don't just walk, but skip and bounce around for fun.
The elderly and people in high places do use it to prefer to younger people and people at lower positions, hence your parents can always prefer to you as đứa at any age.
Here are few terms where you can use it: đứa nhỏ (small kid), đứa bé (little kid), đứa con (a child/an offspring), nhiều đứa (many kids), mấy đứa (those kids, several kids).