"I have small apples."
Translation:Mam małe jabłka.
Why is this form of Apple feminine while up to this point apples have been considered neutral?
It's not feminine. In plural there are only two genders: masculine personal plural and everything else. This means you can use 'małe' with nouns such as 'psy' (dogs - masculine, but not personal), 'kobiety' (women - feminine), 'dzieci' (children - neuter) etc.
On the other hand you would say 'mali chłopcy' (little boys, masculine personal), 'mali mężczyźni' (little men), 'mali ludzie' (little people), etc.