>> This seems unusual to us, so I wanted to ask if anyone else
>> has heard of honey bees stinging birds.
 
Bees will sting anything when they get upset.  It sounds like the bee flew
into the baby, got disoriented, and stung out of reflex.
 
Last month, we had some puppies at the house, and they got stung every now
and then too.. just stumbling into the wrong place at the wrong time (Nobody
suffered lasting consequences luckily).
 
I also know of people who had bees and chickens.  When the bees got upset,
they would sometimes sting the chickens (as well as the beekeeper, his dog,
and the neighbor's cat).  Sometimes the chickens died as a result.