はい、お兄ちゃん、半分こ。

、、。

Here you go, big brother — half for each of us.

Literal

Here, honorable-big-brother, half-[split-こ].

はい as a sentence-opener is the interjection 'here you go' when handing something over (distinct from はい 'yes' as an answer). 半分こ uses the childish suffix こ (also written 子) that casually nominalizes and personalizes — 半分こ is a set kiddy phrase for 'splitting it in half, one for each.' お兄ちゃん is the affectionate address 'big brother' (prefix お + ~ちゃん).