Without a doubt, Edwin Muire, The Horse. I've known it's lines for over 50 years, but still, it brings a tear.
Others of his are also worth a read.
Lines that stick (for a lot of years) in my head include
"And the killing beast that cannot kill
Swells with fury, until
You'd almost think it was despair"
the predator (or something similar)
And
"That I can go out
Go out without a doubt, my father says is the miracle"
On a child dying, I think.
But there are so many poems and poets, that your child could look at. Benjamin Zachary poems were reproduced around a city I once worked in. They were also magic.