Normally a clear blue sky and the hum of bees stand for ease and a good day. Here the poem turns that around. In just three lines, it says that children in Waziristan are afraid of exactly these things.
The poem doesn't spell out why, but the setting gives a strong hint. Waziristan is a region in northwest Pakistan, and the poem seems to point to the threat of attack from above. A cloudless sky offers no cover, and the buzzing of bees may sound uncomfortably like the drone of aircraft. That is an inference from the words and place, not something the poem states.
The speaker stays quiet and observant, simply reporting what the children fear without commenting or raising their voice. That restraint makes the poem hit harder. The mood is uneasy and sad, with a gentle surface covering something dark. The poem leaves us thinking about how fear can ruin ordinary, beautiful things.