
Where are the doors? Is this some sort of futuristic bus where people are beamed inside a la Star Trek? Of course not. Simple logic will tell you that the doors are on the other side of the bus. Mr. Spock would be pleased.
Now consider which side of the road the bus is on. People in America drive on the right side of the road, so you can assume this is the "right side."

Of course, if you're in the UK or another country where people drive on the left side of the road, everything is reversed and the bus is actually going right. Therefore, the bus is going in both directions, being stretched through time and space, forever and ever.
Now, do this simple logic problem in your head in less than a second, like any 10-year-old can.
Children are much better at taking in the first visual cue given and making a snap judgement based on that cue. Adults, on the other hand, take in different visual and other sensory cues before coming to a final judgement — making their decisions slower and perhaps more thought out (though there were no specific figures as to how many adults were stumped by the problem).