What causes stammering?
It isn't possible to say for sure why a particular child starts stammering, but it isn't caused by anything the parents have done.
Developmental and inherited factors may play a part, along with small differences in how efficiently the speech areas of the brain are working.
Speech development
Speech development is a complex process that involves communication between different areas of the brain, and between the brain and the muscles responsible for breathing and speaking.
When every part of this system works well, the right words are spoken in the right order, with correct rhythm, pauses and emphasis.
A child learning to construct simple sentences needs practise to develop the different speech areas in the brain and lay down the neural pathways ("wiring") needed for the different parts to work well together.
Talking problems can occur if some parts of this developing system aren't quite co-ordinated. This can cause repetitions and stoppages, particularly when the child has lots to say, is excited, or feeling under pressure.
As the brain continues to develop, some of these problems resolve or the brain is able to compensate, which is why many children "grow out" of stammering.
Sex differences and genes
Stammering is more common in boys than girls. Differences in brain development between the sexes might make boys more vulnerable to speech and language difficulties.
Genes are also thought to play a role. Around two in every three people who stammer have a family history of stammering, which suggests the genes a child inherits from their parents might make them more likely to develop a stammer.