Of course some of the groups are well known, but does that mean they're the best places to give? Not necessarily. I'm not implying that the charitable organizations are dishonest, though some, especially new ones, might be. But some of the big groups spend so much on overhead expenses like paying a large staff, a lot of office space, extensive advertising, etc. that only a small portion of donations actually reaches the people who need help. Someone I know from Haiti suggests giving to the Lambi Fund www.lambifund.org because nearly all the money they take in goes directly to the people of Haiti. However they aren't involved in emergency assistance and any donations to them will be spent to help the country recover when the emergency situation is over.
It takes time to research an organization to be sure they're legitimate and that the donations will be used in the most practical way. If you don't have time to do that please don't let it discourage you from giving. If the charity is legitimate at least some of your gift will be spent as needed and every little bit helps. If everyone in America gave just one dollar the total amount of donations would be in the millions.
And this is a wonderful opportunity for parents and teachers to help children learn the importance of helping others.