If I got that right, 'lille' is only used for males. 'Lilla' can be used for both, males and females. Since 'pojke' means 'boy' and a boy is a male child, you can use 'lille' but I think 'lilla' would have been accepted as well.
Please corect me if I'm wrong, I'm anything but not a native Swedish speaker.
The adjective endings have an unstable history. Nowadays -e is exclusive used for male things like kings, boys, men, male dogs etc. In older texts, you'll even see things like hundarne, pojkarne and drängarne instead of -arna for nouns that were gramatically masculine.
It's falling out of use now due to a) laziness and b) politics.
However, -e used to be used sometimes as a plural interchangably with -a in 'Standard Swedish', and as a general definite adjective ending. Like in Norwegian, lots of vowel sounds became weakened and lazier, hence -a to -e. But because of language planning, -a is what you use in standard writing and speech.
The text you used is not standard. It still has distinct feminine declension, i.e. katta - katten, natta - natten, broa - bron. It also has ho instead of hon. If I were to hazzard a guess, I'd say the dialect is a western one, somewhere near the Norwegian border.