Children less than what age should not be given honey given suseptibility to botulism poisoning?

1 year old. There's been some recent banter in the literature regarding the use of honey as a cough suppressant in kids given the ineffectiveness and adverse effects of over-the-counter preparations for coughs and colds. However, definitely don't consider this option in children less than 1 year of age.

Of note, 10-25% of infant botulism cases can be traced to ingestion of honey; approximately 10% of randomly selected commercial containers of honey harbor botulinum spores but no toxin. Infant botulism usually occurs between 2-6 months of life.

Source

Paul IM et al. "Effect of honey, dextromethorphan, and no treatment on nocturnal cough and sleep quality for coughing children and their parents." Arch Pediatr Adolesc Med 2007. Dec; 161: 1140.

Jenson, Pediatric Infectious Diseases: Principles and Practice, 2nd ed.