Is it healthy for children to take part in marathons?

A nine-year-old boy is hoping to raise $1m (£655,000) for charity by running a marathon on every continent by the age of 11.

Nik Toocheck from Pennsylvania has already ran in North America and is flying to the Antarctic on Friday. He runs five miles a day, three times a week with a ten mile run every weekend.

BBC Radio 5 live Breakfast asked Dr Keith Tolfrey, a senior lecturer in paediatric exercise physiology at Loughborough University, if if was good for children to run so much.