Two of the child’s siblings have already been confirmed as having botulism, after they were taken to hospital last week.
They had all eaten a Loyd Grossman-branded korma sauce, made by Premier Foods.
Health chiefs said the child is in the Royal Hospital for Sick Children in Glasgow with suspected botulism and that further investigations are being carried out.
The two siblings, from the Forth Valley area in central Scotland, were admitted to the same hospital last week. Their condition is said to be improving.
NHS Forth Valley said the suspected source of the botulism for the new case is the same jar of sauce used by the family.
The Food Standards Agency has advised people not to consume jars from a batch of the sauce, which it has recalled from shop shelves. The recalled 350g jars have a best-before date of February 2013 and bear the code 1218R 07:21.
Only one jar from the batch is known to have been contaminated with the bacteria that causes botulism.
Botulism is rare in the UK and is caused by toxins produced by the bacterium Clostridium botulinum, which attacks the nervous system. The infection is not contagious.