It absolutely is an issue for children. The botulism toxin can be destroyed with heat, but the spores are significantly more resistant to it. And as the WHO exp

It absolutely is an issue for children. The botulism toxin can be destroyed with heat, but the spores are significantly more resistant to it. And as the WHO explains, it's the spores that are the root of the problem for children: "Infant botulism occurs mostly in infants under 6 months of age. Different from foodborne botulism caused by ingestion of pre-formed toxins in food, it occurs when infants ingest C. botulinum spores, which germinate into bacteria that colonize in the gut and release toxins. In most adults and children older than about 6 months, this would not happen because natural defences in intestines that develop over time prevent germination and growth of the bacterium."