翻訳 - 日本語-英語 - ヒマそうな部員連れて食いに来てやったぜ. ここのバイトの子? ...

Better:

Some members looked like they had nothing to do, so I took them to eat here.

(Are you/Is she) Working part-time here?

Hey! Am I the only one who has noticed? What, are you all idiots?
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Notes:
1. The "members" can be members of anything, they don't have to be "department staff."
2. Although this sentence has no verb, it is a direct question to someone, about whether a certain girl/woman is "working part-time here."
3. This should be present noticing, not past. (This was very hard to put into colloquial English, so I had to change the structure of the sentence a little.)

Cucumis should have a way to contact the person requesting the translation to confirm aspects that are unclear. This request has many unclear aspects.

1. He changed it to plural. Japanese does not have plural, and we do not know if it is one or several staff. That's why I chose the word "staff".

2. The girl working part time here? is OK. "Are you" is unlikely to be suitable. It's not a direct question to the girl. 子=girl in this case.

3. Very few Japanese will ask "Are you all idiots?". This is probably referring to other "idiots" not present. I suggest my original translation for this.

Hi cj,
If you want to contact the requester, just click on their name in Green ("silverkleks" in this case) and then leave a note in their Inbox. Even better, just leaving a note here, under their translation request, should get their attention. (They might not reply very soon, though, especially if it an old request...)
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Your translation is okay, and so I have not changed it except for the addition of "have" in the last sentence, to reflect the immediacy of the comment.
Other notes:
1. The word "staff" means all the members on a staff. The text here does not say "all the members," but it is not impossible that it was all the members, so I have not changed your translation here.
2. I can easily imagine a case where the customer looks up from the newspaper or manga he is reading and asks the waitress「ここのバイトの子? 」. Or he might be asking someone else about her. Anyway, this is a direct question.
3. "Normal Japanese people" would never say this sentence in the first place, even implying that everyone else are idiots. This "tough guy" Japanese way of speaking ないね changed to ねぇな means that the speaker could indeed perhaps be the kind of person who would call other people idiots for not noticing something he has noticed.
Don't worry, I realize I have a 外人 face, but I have lived in Niigata for 20 years, and I am fluent in both written and spoken Japanese...

I'm not worried. I guess we can agree to disagree.
By the way, staff can mean 1 person.
http://dictionary.reference.com/browse/staff