(CNN)When adults want a flu shot, they have two choices: go to the doctor or go to a pharmacy.

But in most states, laws prevent parents from just walking into a pharmacy and getting their children vaccinated for the flu. Public health experts say that's costing children's lives.

"Parents should have no barriers whatsoever to getting a flu shot," said Dr. Irwin Redlener, director of the National Center for Disaster Preparedness at Columbia University. "It's what we'd call a no-brainer."

Currently, 40% of children don't get a flu vaccine, and public health authorities are keen to change that. Flu kills children every year; last year, 143 children lost their lives to the flu.