The recommended dose of DayQuil Cold & Flu liquid is: 1  Adults and children 12 years and over: 30 mL (2 TBSP) every 4 hours. 2  Children 6 to under 12 years: 15 mL (1 TBSP) every 4 hours. 3  Ask a doctor before using in children 4 to 6 years of age.