ett barn = a child • ett litet barn = a small child • barnet = the child • det lilla barn = the small child
To make a noun definite when there is no adjective, you simply attach the definite suffix (-en, -et, etc.). When there is an adjective, you have to do three things:
- use the appropriate definite article (den, det, or de)
- use the definite form of the adjective (usually identical to the plural form, but in the case of 'liten' the definite singular form is 'lilla', while the plural form [definite or indefinite] is 'små')
- attach the definite suffix (-en, -et, etc.)
Hope that helps.
små is the plural. It's an irregular adjective. The whole paradigm looks like this:
en liten mus 'a little mouse'
ett litet hus 'a little house'
små hus 'small houses'
den lilla musen 'the small mouse'
det lilla huset 'the small house'
de små husen 'the small houses'
musen är liten 'the mouse is small'
huset är litet 'the house is small'
husen är små 'the houses are small'
It's called double (or even triple) definiteness. You can tell that the phrase is definite from the front article, the adjective, and the noun ending. This is how nouns work with adjectives in general in Swedish. It's hard to give a real "reason" for it but you can think of it as a sort of harmony between the words. Also, redundancy is typical of natural languages, which is practical in many communication situations where you may not hear everything clearly.