i will admit that death is a part of life be it cats, dogs, humans, or fish. But it is not something you should be familiarizing yourself with or your children with, death is not the aim of this hobby. Yes it is a reality that is horrible when it occurs but you make it sound like you are impressing it onto your children so they can handle it like it will occur often.
I admit that my first fish were damsels, but my tank was completely cycled and yes they can be agressive little guys, but they are still in my tank. I love them as much as any of my other fish and I would be just as sad if one of them passed away as I would be if my porc puffer passed away.
You can't play favorites with life and say that my dollar damsel's life is a sacrifice for my $100 fish's life, that just isn't right.
You have very little money invested in this fish, give it away, take it back to the store, don't flush it because it's served its purpose.
Death may be a part of this hobby but it is a part that most of us try everything in our power to avoid.