Intermittent leave for children over 18

Can someone point me in the right direction?

I have an employee who has requested intermittent FMLA to take her teenage daughter to appointments, hospital visits, etc.

As I was preparing the paperwork to offer provisional FMLA, I noticed that my checklist says "to care for spouse, child, or parent with serious health condition and child must be under the age of 18 unless mentally or physically disabled." The daughter is 19 years old and is not disabled.

Is there something in the federal regs that actually states that FMLA only covers children under the age of 18?