I don't give money to beggars anywhere in the world but I do have a "Charity Budget" whenever i travel, This budget will go to a Charity organization etc... orphanage.
Why? You are showing them and/or giving them an option to continue to live their life on the street,(They see that they can make money by living on the Streets, Many also tend to be in tow of their children, You are also responsible for the child to grew up on the street)and then You might also be responsible for the fact that there are people behind the scenes using this people for their own benefits(Slavery -- Remember Slum Dog millionaire, That IS a true fact of how people use kids/adults and burn and cut them an put them on the streets to beg)
P.s I do buy drinks/food for individuals but no money. I have done that several times in Singapore too.