I assume he begins with; "Forgive me, Father, for I have sinned." The rest is covered by the sacramental seal :D
Jokes aside, the saints who indeed had such a life and whose (auto)biographies have arrived to us realized that the greater the perfection attained, the greater the awareness of their sinfulness. An example: an average sinner like me barely detects mortal sins through a good examination of conscience, and is happy when he can stay a fairly long time without committing such sins. A very holy person would on the other hand suffer greatly even from a venial sin or even from an imperfection, because he is fully (or to a great extent) aware of how terrible it is to offend God, no matter how small the offense!
We sin in words, thoughts, deeds, and omissions. The greater our responsibilities, the more we are likely to sin.
All I can tell you is this: you will never reach a moment in the devout life in which you will find yourself without anything to confess. "If we say we have no sin, we deceive ourselves."
To confess "like a child" to me means to talk to Christ with filial fear, not with servile fear. A servant is afraid of his master because he did not obey him. A son simply feels sorry because he made his dad feel bad, and wants to "make peace" with him and keep making his dad happy.