I agree with HWB.
We should be clear about what are biological reasons and what are purely cultural reasons. Biological reasons are valid everywhere whereas cultural reasons could change from country to country, community to community and from time to time.
According to the dictionary, a person is a child is only from birth to puberty. After that, they are presumably young men and women.
About a 14 year old not being able to give consent.....that depends on lot of things.
1. Under very harsh living conditions people tend to mature very fast. A 14 year old under such conditions may be perfectly capable of giving consent, getting married and having children. Even young children at 7-8 were expected to work and take up responsibilities. (The teddy hugging, thumb sucking archetype is of recent origin and that too only in rich countries).
2. If 14 year old's cannot give consent, they should be at home under mummy's and daddy's care till they are 18 (or 16 or 21 depending on the country

). However that is not what usually happens in liberal western countries.
3. According to statistics, nearly 41% of teens have had sexual intercourse....and perhaps with the full knowledge (and approval or indifference) of the parents. So...when you say they cannot give consent, what exactly do you mean? Does it mean that all teens who have sex are criminals and should be charged with rape?
My point is that there is no consistence at all between the liberal sexual life that most westerners lead and the sudden indignation and wrath at supposed trespasses.