Yep! This is a big issue on pretty much most Minecraft specific content sites & videos. I think these spammers specifically target Minecraft keywords and Minecraft sites through Adwords display ads knowing that kids will click the ads. If your site has Minecraft content and is serving Adsense within that content, you are almost certain to have these types of ads display. Not the fault of the actual content site but an issue with the spammers targeting through Adwords.

It is really common actually on most game content or videos that are geared towards the youth. These Adwords spammers target this category specifically.