I understand mistakes, but sticking one's hand where it doesn't belong is a decision. A 14 year old teenager knows not to fondle little girls, especially family members. This decision is also a lot worse than sneaking into a similarly aged female's house to get laid.
If he did that to one of my family members, I'd give him the 3's treatment with no regrets.
A 14 year old teenager knows not to fondle little girls, especially family members. Again, you are attempting to rationalize sin, and there is no rationale to sin, other than it is evil.