To block out distracting background noise, simply switch on the active noise cancellation which allows the child to listen clearly without turning the volume up needlessly high.

Feedforward ANC measures the noise from outside the ear-cup and generates a cancellation signal equal and opposite to the noise. The cancellation signal is never completely perfect, so , in a hybrid design the Feedback picks up the remaining noise signal inside the cup and adds an additional layer of cancellation. 

Either feedforward or feedback can be used individually in a headphone to produce noise reduction. As they operate essentially independently both can be used in combinations to achieve greater levels of noise reduction than either can produce on their own.