A four year old boy is being treated at Frenchay Hospital near Bristol for serious head injuries after a crash on the A3072 near Holsworthy.
He and a 32 year old woman were in a car, which overturned on the road. She sustained back injuries.
Police would like to hear from anyone who saw the accident, which happened between Weekstone Cross and Weekstone Cottage just after 1pm on Saturday afternoon.
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Hotter again on Monday with temperatures up to 25 degrees. Cooler on the coast and on the Isles of Scilly.
A clear night, hotter again on Monday.
Highs this afternoon of around 23 or 24 degrees. Cooler on the coast.