A freeloading child with 居候

Kanji Explanation:

Conan returns home from school to the sound of a music box. When he opens the door, he finds Kogoro and Ran with a client.

欄(らん):: 「あ、コナン君(くん)　お帰(かえ)り！」; “Ah, Conan, welcome back!”
春菜(はるな):: 「あれ　息子(むすこ)さんもいらっしゃったんですか？」; “Oh? You have a son, too?”
小五郎(こごろ):: 「いえ、こいつはウチで預(あず)かってる居候(いそうろう)で…」; “No, this kid's just a freeloader we're looking after...”

Key Points

1居候(いそうろう) = someone living in another household

Here 居候(いそうろう) describes Conan as a child staying in Kogoro’s home rather than as Kogoro’s son.
The word often carries a dependent or freeloading nuance, which fits Kogoro’s dismissive tone.

2預(あず)かってる = “we’re looking after” or “have in our care”

預(あず)かってる is casual speech for 預(あず)かっている, the progressive/result state of 預(あず)かる.
In this scene it means Conan has been entrusted to the household, so Kogoro is responsible for him but not his parent.

3ウチで marks the household, not just the building

ウチで means “in our household” here, setting where Conan is being kept or looked after.
This supports the contrast with 息子(むすこ)さん: Conan belongs in the home for now, but not as family in the way Haruna guesses.

4Casual correction after いえ

Kogoro’s いえ rejects Haruna’s assumption that Conan is his son.
こいつ is a rough, familiar way to refer to Conan, so the line sounds casual and blunt rather than politely explanatory.

君(くん) is an honorific suffix used after names, typically for boys or men. It’s commonly used by teachers addressing male students, by friends among young people, or by superiors addressing junior colleagues, and can also be used for girls in childhood or casual contexts.