1 The diphtheria, tetanus, and pertussis (whooping cough) vaccine (DTaP) are usually given to babies at ages 2, 4, and 6 months, and again at 15 to 18 months old. 2  DTap is a very effective vaccine for small children. 3  Kids will need another booster between ages 4 and 6. DTaP. 2  The diphtheria, tetanus, and pertussis (whooping cough) vaccine (DTaP) are usually given to babies at ages 2, 4, and 6 months, and again at 15 to 18 months old. 3  DTap is a very effective vaccine for small children.