How is it a bad neighbourhood? Are you making that assumption based on the fact that it is a slum? One of the bar's most frequent patrons is Johnny who has a hard on for Tifa and would protect Marlene with his life; Sector 7 could very well be a close knit community.

The idea that an eight-year-old could be left in charge of the bar is horrific at best, but that is still assuming our standards apply. Besides: it doesn't appear that they have a separate home; perhaps she merely locked the doors and stayed there. Taking her along on a terrorist attack doesn't seem like better parenting. I would have liked to see her go next door and staff with Johnny's family, but again, there is no guarantee that his family didn't look after her anyway given that Johnny was leaving town and they would be without a kid for the first time in forever.

Also, yeah, sometimes there are bigger fish to fry.

Elmyra
"You're her father!? How in the world could you ever leave a child alone like that!?"


Barret
"...please don't start with that. I think about it all the time. What would happen to Marlene, if I..."
"But you gotta understand somethin'... ...I don't got an answer. I wanna be with Marlene... But I gotta fight."
"'Cause if I don't... the planet's gonna die."
"So I'm gonna keep fightin'!"
"But, I'm worried 'bout Marlene. I really just wanna be with her... always."
"See? I'm goin' in circles, now."

No point protecting your daughter if she's gonna die along with everyone else far before their time, right? If you've got the power to fight, isn't it your responsibility to do so?