In "The Scarlet Ibis," why does the family not help bury the birds?

Doodle’s mother does not want to bury the dead scarlet ibis because she is afraid it will carry a disease. 

It makes sense that when a strange exotic bird comes into your yard and dies, you might want to avoid coming in contact with it.  Doodle has an affinity with the bird, a rare scarlet ibis that is miles from where it should be, and feels sorry for it.  He certainly understands sickness. 

Doodle leaves his food and comes to kneel by the bird, but this makes his mother nervous. 

Doodle remained kneeling. "I'm going to bury him."

"Don't you dare touch him," Mama warned. "There's no telling what disease he might have had." 

The whole family feels sad for the bird, but Doodle already has a compromised immune system and his mother does not want to risk him getting some exotic disease from the exotic bird.  She doesn't offer to have his father will bury it for Doodle, so Doodle takes it upon himself to bury the bird.

Doodle manages to bury the bird without touching it as the family watches from the table.  He lifts the bird’s head with a string and slowly drags it while singing a funeral dirge.  He then struggles to dig a hole to bury the bird. 

His awkwardness at digging the hole with a shovel whose handle was twice as long as he was made us laugh, and we covered our mouths with our hands so he wouldn't hear.

The bird foreshadows Doodle's fate.  As strong as he is, Doodle is just too exotic for Earth.  His brother pushes him too hard, and Doodle collapses just like the bird.  Perhaps he knew when he was burying it that he might share the same fate someday.  Doodle never was strong.