We use a plural noum for different things, like trousers, pyjamas, glasses, binoculars, scissors.
I left my pyjamas in Ibiza.
My sun glasses are broken.
My news trousers are reds.
Diferents noums haven diferents words for singular and plural. Foot-feet, tooth-teeth, man-men, woman-women, child-children, person-people.
The children go to school every day.
This child has blue eyes.
Many people go to work by bus.