It is sad when pets die - especially when they are young. I have had little kittens die for no apparent reason, which is one of the reasons I am not doing SPCA fostering right now. It turned out that we - and a number of other fosterers - had got infested with a bug that is very fierce on babies. The older they are, the better they can survive it. And I was trying to keep them confined in a cage, which you can't really do when they are older & able to run around.
Will you replace the duckling? And the chicks? Or do it again next year?

A lot of fun, & really interesting.