From cute cuddly bundles of joy to teenagers bursting with emotions and spots, we'll learn that by the age of five we have all of our brain cells, and find out the truth about why boys' and girls' brains develop at a different rates.
Sienna is one example of a girl who at the age of five saved her mum's life after she collapsed at home. Sienna called the emergency services from the home telephone so they could trace her address - such logical behaviour isn't thought to occur until adolescence usually, but new research is proving otherwise.
As we move on through puberty to the teenage years, many questions will be posed - just why do teens stay in bed until midday?! And what makes them love to do risky, dangerous things?
Secrets Of Growing Up, ITV, 9pm
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