Sorry but this is outright sexism. Males, even young males, can enjoy looking after children without any ulterior motive. You wouldn't be asking the same question about a 17-year-old girl, I bet.
Views like yours are a big part of the reason many men are such poor fathers, because they've grown up believing that caring for their children properly is somehow unnatural.
Maybe the statistical risk of abuse is too high to allow men in childcare settings, but to imply any man who would like to have a nursery job must be a pervert is an awful, outdated attitude.