Translation:The child has several blue pencils.
why can't you say "the kid has some blue pencils"? In this manner "some" means "several" or "a few".
Maybe I'm misunderstanding, but I thought ребёнок and ребёнка meant male child and female child. How come duo keeps dinging me for translating these as "boy" and "girl" respectively?
Because they don't mean male and female child. ребёнок means child. ребёнка is the genitive/accusative. (In this Duo sentence it's genitive.)