There are two billion children (small people under the age of 18) in the world. But since Santa doesn't (appear to) handle most non-Christian children, that reduces the workload to about 15 per cent of the total (roughly 378 million according to the Population Reference Bureau). At a rate of say, 3.5 children per household, that's 91.8 million homes. One presumes there's at least one good kid in each.
Santa has 31 hours of Christmas to work with, thanks to the different time zones and the rotation of the earth, assuming he travels east to west. That's 822.6 visits per second. For each eligible household, Santa has 1/1000th of a second to park the sleigh, jump down the chimney, fill the stockings, put presents under the tree, eat any snacks, kiss mommy when available, get back up the chimney, hop in the sleigh and move on.
Assuming each of these 91.8 million stops are evenly distributed around the earth, we're now talking about 0.78 miles per household - a total trip of 75.5 million miles, not counting stops to let Santa and the reindeer do what most of us must do at least once every 31 hours. This means Santa's sleigh moves at 650 miles per second, or 3,000 times the speed of sound. The fastest man-made vehicle, the Ulysses space probe, moves at a poky 27.4 miles a second (a conventional reindeer, by the way, can run 15 miles per hour, tops).
Assuming each child gets nothing more that a medium-sized Lego set (two pounds), the sleigh is carrying 321,300 tons, not counting overweight Santa. Conventional reindeer can pull no more than 300 pounds. Even granting flying reindeer could pull 10 times the normal amount, Santa would need 214,200 reindeer. This increases the payload (not counting the sleigh) to 353,430 tons, or four times the weight of the Queen Elizabeth II. 353,000 tons travelling at 650 miles a second creates enormous air resistance, which would heat the reindeer to incandescence in the same fashion as spacecraft or meteors entering the earth's atmosphere. The lead pair of reindeer will absorb 14.3 quintillion joules of energy. Per second. Each. In short, they will burst into flame almost instantaneously, exposing
the reindeer behind them and creating deafening sonic booms. The entire team will be vaporized within 4.26 thousandths of a second.
Santa, meanwhile, will be subjected to centrifugal forces of 17,500.06 gravities. A 250-pound Santa (a wee bit of an underestimate) would be pinned to the back of his sleigh by 4,315,015 pounds of force.
The Internet originator's conclusion to the above: "If Santa ever did deliver presents on Christmas Eve, he's dead now."