I did some research on this recently because my son just turned 1 year old. It seems as though the recommendation not to give honey to an infant comes from some scientific research done a few decades ago, which found a slightly increased risk of illness. However, if I remember correctly, pasturization was thought to be an effective counter-measure. Apparently, no body has done any research to prove that pasturized honey is safe for infants, so the recomendation has continued to not feed any honey to infants.
Pasteurisation, if done correctly, will destroy the toxin but may not get rid of the bacterium - this is because the spores are resistant to heat.
The risk is that infants in the first few months of life have not fully developed their gut defences, so the spores can colonise within the intestine and release the toxin.
In older children and adults, any spores will be annihilated during passage through the digestive system, so it is safe for them to consume honey.
