They would say:
Variant #1). Santa can change laws of physics.
If the respectable publick says :"Naaa...", then:
Variant #2). Santa can warp space, and stretch time, so all children are actually within few microns from each other (For Santa, not for them!), and thus Sant can move quite slow (he can even remain drunk and still be able to process all requests). This hypothesis is strongly supported by observations: Santa was observed to have red nose. So, this seems to be the way Santa works.
Variant #3). If still someone doubts, another relativity idea may come to resque Santa's reputation. May be he can move FTL! Then he can go back and forth in time at an arbitrary time intervals and thus appear near each child's place at any required by time zone time moment. He even may go back to East (or to North?) to refill his supply of latest Nintendo (or Sony) CDs and rare to find items.
If even this won't work for some sceptic minds,
Variant #4) Santa obeys all laws of physics, but he is NOT made of fermions (atoms, etc) - only of bosons (photons, gravitons, etc). Thus, his mass is zero, his inertia is zero, thus he can move with speed of light c, and instantly change the direction of motion like a light reflecting from mirror. This hypothesis is also 75% supported by obsevations - Santa usually stops with much higher probability where dark matter is (sooth in chimney). If there is no fireplace, Santa can be stopped with 24% probability by some absorbing the middle part of visible light spectrum substance (green x-mas tree, for instance) and may drop orders there. Othervise he just bounces (reflects) to the next better equipped by santa stops house.
Variant #5) Santa has so strong psi-function, that even small portion of it appears to children as a full-scale, full-color Santa. So, while most of Santa is still on East pole (generating toys), some portions of this Santa are present near each and every house which had ordered toys and paid for the orders on time.
So, there are still some physical (or not very if you don't like physics) ways Santa can deliver goods to all children on time.