It's possible for kids to catch whooping cough even after they've been vaccinated.
My sister and I caught it when we were quite young, even though we'd had all our shots. My Dad had just been transferred to Mackay and we were on our way there when we got stranded between two flooded rivers for three days. My Mum had quite a stressful time, especially when she saw us sharing a softdrink (through a straw) with some other kids!