I saw in the newspaper where kids are hitting puberty at earlier ages. The article mentions a few things like obesity as being the cause. The real cause is nutrition via foods that disrupt the hormonal axis.
Cordain wrote about this probably ten years ago. You can also look at modern hunter-gatherer tribes and find that their children do not enter puberty early. The bigger problem is that hitting puberty early also predisposes a person to various cancers.
Luckily, there is a simple solution to all this: make sure kids eat real food!