From the time our kids are born, there are (usually) two primary caregivers- Mom and Dad. If the baby is lucky enough, there are more...grandparents, aunts, uncles, god-parents, siblings, etc, but let's primarily consider the parents at this point. As the child grows, parents are constantly saying things such as, "You got it!" "Good girl/boy!" "I love you." "C'mon, the peas aren't that bad..try again." "Come to Momma/Daddy...you can make it. Just a few more steps!"
Parental encouragement develops confidence in the very young and continues throughout the child's life. Even at my age, my mother is still encouraging me to "follow my heart" or "do my best." I don't think she'll ever stop telling me such words. It's in her maternal nature.
Once the child reaches school-age, those who boost his confidence can include teachers, librarians, coaches/activity instructors, music instructors, friends, principals, even his doctor or dentist. Who doesn't love to hear that all is GREAT at a doctor and/or dentist visit? No cavities means Little Johnny is doing a GREAT job cleaning those teeth! There are more and more people who are influencing and encouraging the child -- confidence now is not just reliant on the parent(s) or other family members.
Throughout the school years, however, the child does begin to develop their own sense of self-confidence. Whenever they have a new experience--whether it's the first day of the school year, taking a test, visiting a new friend's house, trying out for a team, joining a club--the more the child has these experiences, the more self-confidence he will have. Repetition of similar experiences not only makes things appear easier, they allow the child to want to try something different.
Since I'm only the expert of my own children, I can tell you that I see this time and time again with my two boys. My younger son is the polar opposite of my older son. Son #2 is very smart, very cerebral, and is always concerned with the "big picture". He's very black and white, so gray areas confuse him or make him uncomfortable. He has tried many sports, and although athletic, none have ever captured his attention. He would rather play his trumpet, fool around on the piano, or play a video game than engage in backyard football. And don't even talk to him about hockey! He consistently scores above 99% on most standardized tests and probably should be in a gifted school. Given his academic talents, you would think that he was the most confident kid. Guess what? He wasn't confident until this past summer. Oh, by the way, he's 13. That seems sort of old, in my mind, to be just finding his confidence in "life", especially when his older brother seemed confident when he started running at 7 months instead of walking. But, after spending twelve days at a fine arts camp, Son #2 was so confident, he seemed like another child when my husband and I picked him up.
What's my point in all of this? I believe that parents are the primary confidence-builders for their kid, but that each person who encounters that child is also partially responsible for building or breaking that child's confidence. Eventually, the child will gain enough self-confidence that minor confidence-breakers from adults/authority figures will just be blips to them and won't produce the devastation of fulling losing their confidence.
How are you a confidence-builder?