Is it dangerous if toddler swallows long hairs?

Hair: Not unless they swallow massive which can form a bezoar (massive cluster if hair) which can cause a bowel obstruction.

Eating hair: If a child swallows a long hair or two if a child is eating hair regularly he/she can develop something called a bezor which is a collection of material- in this case hair- and that could create a blockage in the intestine.