Tifa is a horrible character and totally unrelatable and irresponsible (who leaves a five year old in charge of a bar?!).
Imma come off as a total Tifa fanboy but Barret shares the larger part of the resposibility. And you're assuming they have the same norms regarding children on the Planet. Or in the slums for that matter. When you're poor you use any helping hand you got, even if it's a 5 year old's. Heck Reeve decided post-AC that children won't be able to join the army like it's a ground breaking innovation.
That said, a lot of the things Tifa chooses to do is indeed questionable. *coughCloudsmemorycough*
And erm, my last unpopular opinion: Tifa and Rufus are meant to be together. Should guarantee me at least second place?