Here is an excellent explanation: https://en.wikipedia.org/wiki/Swedish_grammar#Articles_and_definite_forms
Here is a chart I made for myself:
- en liten pojke (a little boy),
- ett litet barn (a little child),
- den lille pojken (the little boy),
- det lilla barnet (the little child),
- många små pojkar (many little boys),
- många små barn (many little children),
- de små pojkarna (the little boys),
- de små barnen (the little children), So, små is used in plural, while lilla is used in definite form
Wondering about difference between lille and lilla?
"The -e ending is strictly masculine. It's a remnant from when Swedish still made that grammatical difference, but today can only be used for actual masculinities. The -a ending can be used for anyone, though, and is by far the most common. I recommend sticking to it if at all unsure (so you can refer to a little boy as "den lilla pojken")."