Nick Maclaren wrote:
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I would (and did) take the "chemical burn" plants more seriously than
the "poisonous" ones. If a child gets the sap on its hands, and rubs
its eyes, that could be VERY bad news. And that is actually a likely
scenario, unlike a child munching random unpalatable leaves, digging
up and eating roots etc.

Unfortunately, there are a fair number of such plants. Giant hogweed
is one; all sumachs and euphorbias are others - and the last include
petty spurge (a very common weed) and the house plant "poinsettia".
Also periwinkles, but mere touch isn't enough to reach the sap.
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While the saps of Toxicodendron (poison sumac(h)s) are highly
allergenic for most people, do you have a cite that shows that all
other sumachs have "toxic burn" saps?