When David muses that he would be sorry were any child to exchange, "the simple confidence of a child, and the natural reliance of a child upon superior years" for "worldly wisdom" (69), what does he mean in David Copperfield?
For a child to stop trusting adults, he has been tricked and mistreated by them.
The older David is reflecting on how as a child he trusted the waiter, because he was older, and the waiter tricked him out of most of his meal.
When David is sent off to school after he is brutally beaten by Mr. Murdstone (because he bit got fed up and bit him), he stops at an inn where an over-obliging waiter manages to advise David out of most of his dinner and a lot of his money.
For example, when he pours David his ale, he tells him a colorful story about a man who died from drinking it.
I was very much shocked to hear of this melancholy accident, and said I thought I had better have some water. (ch 5)
When the adults joke about how much David ate, he begins to suspect the waiter.
If I had any doubt of him, I suppose this half awakened it (ch 5).
This is one of the first times little David begins to stop trusting adults. Before now, despite how the Murdstones treated him, he trusted adults.
There is a bit of Dickens narrating in this sentence. The book is the story of how naive David is, and how he is continually taken advantage of. With each person that takes advantage of him, David gains more wisdom. However, it is hard-earned wisdom because he loses his faith in people.