Fluoride-containing toothpaste can be acutely toxic if swallowed in large amounts, but instances are exceedingly rare and result from prolonged and excessive use of toothpaste (i.e. several tubes per week). Approximately 15 mg/kg body weight is the acute lethal dose, even though as small amount as 5 mg/kg may be fatal to some children.
The risk of using fluoride is low enough that the use of full-strength toothpaste (1350–1500 ppm fluoride) is advised for all ages. However, smaller volumes are used for young children, for example, a smear of toothpaste until three years old. A major concern of dental fluorosis is for children under 12 months ingesting excessive fluoride through toothpaste. Nausea and vomiting are also problems which might arise with topical fluoride ingestion.
Read more, here.