This is that stage in your kid's life, he may get mood swings every now and then. As he is growing, his exposure to the world is increasing making him liable to a plethora of emotions. This will obviously lead to mood swings in scenarios where he is tired or upset over something that happened at school. 'After school grumpiness' is a common situation that can creep up every now and then among kids.
What you need to know:
It is upsetting to see that the happy child you dropped off to school, has come home in a completely opposite mood. Quiet children who are speaking in monosyllables is a common view at homes after school hours. The reason behind this behavior is the sheer exhaustion of a long day. Young children find it easy to get tired in a couple of hours. After coming home, this tiredness may make your child irritable. The best way to deal with this is to feed your child peacefully. Allow him to relax by going for a walk. A short nap can work wonders as well. Remember not to bombard questions at him but deal with him in an understanding manner.