Parents who want to put their toddlers in pre school will have to make sure their kids get their shots first.

The health department approved a measure Wednesday that mandates that any child under 5 must get the flu vaccine if they want to enroll in a day care program. Health Commissioner Thomas Farely said one out of four city kids contract the virus, which is harsher for them due their weak immune systems, and a third don't get the vaccination.

The flu symptoms are also bad for the rest of the population, according to the commissioner.

"Young children often pass influenza to other children and family members, who then spread the infection to others in the community. This mandate will help protect the health of young children, while reducing the spread of influenza in New York City," he said in a statement.

The mandate will go into effect for the 2014-2015 school year.

Schools and day cares that fail to provide documentation that their students were vaccinated by December 31, 2014 will be fined, according to the health department. Kids with health or religious issues that prevent the vaccination are exempt.