What is the meaning of [The child is father to the man]

“A child’s character is an indication of the type of adult he or she will become – human nature does not change from youth to maturity.”,Martin H. Manser (2007). The Facts on File Dictionary of Proverbs. Infobase Publishing. p. 388. ISBN 978-0-8160-6673-5. Retrieved on 1 August 2013.