Why do people have issues with shipping (fictional) minors in media?

For those who may be unaware, "shipping" is when fans of a piece of media believe two (or more) characters should get into a relationship or like the idea of them being in a relationship.

I am an avid shipper. In almost everything I consume, I will usually end up shipping two characters. This goes for anyone of any age. However, something I keep encountering is people calling it "weird" if you ship two kids together. I have never understood this, and I can't comprehend what would be weird about it. Lots of kids date in real life, so it's not abnormal.

Please enlighten me.

Edit: 6 replies and the majority have just been saying it's weird. I hate reddit.