Most people believe that if we collect money and give food for Orphans (I am Sorry to day this) for a day is not enough. I understand it but the intention must directed towards supporting organizations who already serving orphanages.
Firstly one has adopt an orphanage. After that collect and fund money for that orphanage. Try to spend your free time with those children and try to teach for the lower classes (as a teacher). After a while with your valuable services, one has the CHANCE to join a street children in that orphanage/organization.
But there are Several points to discuss here about street children:
1. Not all street children are home less, some are escaped from home. If we have will, we can get them back to home.
2. Some street children are robots in the hands of some anti social elements for earning money.
So if you adopt an orphanage in one way you are serving the organization/orphanage and in other way you have a chance to join children in streets in the orphanage.
REMEMBER, Doing all this is not a one day effort but has to be done with LOT of Dedication. Please do dedicate some of your life time to serve humanity.