The requirement that children under 19 be granted insurance regardless of preexisting conditions has caused Blue Cross and Blue Shield of Florida and many other insurers to stop offering child-only coverage.

A key difference between the two provisions is that employers generally insist on a limited open enrollment period during which workers must sign up for coverage for themselves and their families, said Robert Zirkelbach, spokesman for America’s Health Insurance Plans, the industry’s trade group.

Arguments about the constitutionality of health care reform reverberate through courtrooms in Florida and across the nation, two provisions that have already kicked in are sparking opposite reactions from insurers.

Insurers fear they will lose money because parents might sign up for coverage only when their children become sick. That is scheduled to change in 2014, when the law requires that virtually everyone have health insurance — a provision that a federal judge in Pensacola declared unconstitutional on Jan. 31.

But the provision requiring many employers to insure adult children up to age 26 through their parents’ plans has glided into practice with virtually no opposition because health care consultants, insurance companies and major employers believe cost increases will be minimal and benefits widespread.