There are about 2 billion children of the age 18 or below in the world, but since Santa Claus will ignore those believing in Islam, Hinduism, Judaism and Buddhism (except Japan), therefore according to the data from Census, the workload of Santa Claus includes only 15% of all the children, i.e. 378 million. According to statistics, there are on average 3.5 children in each family, so if we assume that there is at least one good child in each family, then Santa Claus has to go to 108 million families.
Thanks to the self rotation of the earth and different time zones, if Santa Claus starts his journey from the East, and goes along to the West, then he would have around 31 hours of Christmas to finish his job. In this period, he must visit 967.7 families per second, i.e., putting the gifts in the stockings, placing the remaining gifts under the Christmas Tree, climbing up the chimney, jumping on to the sleigh and depart for the next family.
For simplicity, let us assume that the 108 million families are evenly distributed on the surface of the earth. Then, the average distance between 2 families are about 780m, and the whole journey is as long as 75,500,000km, and this doesn’t include taking rests and going to bathroom. Therefore the Santa Claus’s Sleigh needs to travel in a speed of at least 650km/s, about 3000 times the speed of sound. Comparatively, the fastest ever artificially accelerated solar probe - Ulysses, travels at a sluggish speed of 27.4km/s only. Superman can fly at 1km/s. An ordinary reindeer at most can just run at 15km/h.
There is another issue about loading. Assume that the gift that each child receives is just an ordinary Lego package (about 2 lb), then merely the gifts will consist of 500,000 tons. On earth, an ordinary reindeer can pull a weight of 300 lb. Assume that a flying reindeer has 10 times the power of an ordinary one, then Santa Claus still requires 360,000 flying reindeers to transport the gifts. But the total weight of 360,000 flying reindeers itself weights over 54000 tons, together with a sleigh that can afford such a weight of loading, this makes the total weight over 600,000 tons. This is about the weight of 30 Godzilla, or 78 Queen Elizabeth Ocean Liner.
Similar to a space shuttle traveling back to earth, an object of 600,000 tons traveling at a speed of 650km/s in the atmosphere will have friction with the air and generate heat. The 2 reindeers in the front of the group will absorb 1.43 x 10^19 Joule energy per second, this make the poor reindeers explode in an instance, and the power will involve all the other reindeers behind and all of them will explode into ashes. Furthermore, the Ultrasonic wave pulse generated by traveling at 3000 times the speed of sound will destroy all the troop of reindeers, the sleigh and the gifts, everything will dissipate into thin air in the period of 0.00426 second, this is exactly when Santa Claus reaches the 5th family.
However, all of the above are not important anyway. This is because when Santa Claus accelerated from rest to 650km/s in a period of 0.001 second, (recall that Santa Claus need to visit about 1000 families in 1 second) he must withstand 17,500G of gravitational acceleration. Even if Santa Claus is as slim as 250 lb only, he will still be crushed onto the backseat of the sleigh by 4,315,015 lb of pressure acting on him, crushing his organs and skeleton in an instance, leaving only a mince of meat.
Therefore, if there were Santa Claus, he would be dead.
This is what you should all be drinking. Not that poncy bottled shit that costs a thousand times as much and has been shown to harbor lots more nasty bacteria. 
