Nitrosatable compounds can be converted into nitrosamines, which are genotoxic carcinogens via inhalation, ingestion or dermal exposure. A child could become exposed to them by putting the product in the mouth.

Most nitrosamines are carcinogenic in nonhuman animals. A 2006 systematic review supports a "positive association between nitrite and nitrosamine intake and gastric cancer, between meat and processed meat intake and gastric cancer and oesophageal cancer, and between preserved fish, vegetable and smoked food intake and gastric cancer, but is not conclusive".

Source and more information: https://en.wikipedia.org/wiki/Nitrosamine