The PRIME mystery of solving the puzzle of parenting is: why is my child so irritable? It is normal for children to get fussy or whiny sometimes. Being fussy is as if they're birth-right, we often think its because they want our attention.
However constant or prolonged bouts of irritability in school-going children can be a deterrant in their focus and social skills (generally their growth). Thus this could be due to these reasons:
Lack of sleep
Unable to comprehend what they want
Quarell with a sibling
Being too hot or too cold