It depends on their age and whether they are traveling with a parent or guardian who has enrolled in TSA PreCheck: Children 12 and under may accompany an enrolled parent or guardian in the TSA PreCheck lanes without restriction.
Do I need any documents for my infant to fly?
Employees may ask for age verification at any point, so please travel with a copy or original form of any government-issued ID, such as a birth certificate or passport for your child. A medical release for travel is required for any infant under 14 days old.