<<Disclaimer: Verify this information before applying it to your situation.>>

Regarding the kindergarten child with CD whose teacher suggested that the
child stay home if they could not participate in the project due to
contamination.......

Ask the principle and teacher if they comply with federal law such as IDEA.
In essence, individuals with disabilities are entitled to a free public
education in the least restrictive environment.  Individual plans must be
made for each child who qualifies as to how the school will accomplish that
mandate.  CD children should qualify and forcing the child to stay home
rather than modify an art project sounds like a great  court case.

Good luck and fight on!