Mycroft Holmes doesn't trust babies.

Certainly, they are adorable when they are first brought home. Their seven year old brother can't be blamed for being curious about them. How is he to know, that the moment the tiny, fully-functioning human being is put into his arms, he will be overwhelmed by the trust the tiny human is showing in him by sleeping peacefully in his arms? And that he will feel obliged to justify that trust by committing himself to said baby's welfare?

The older brother cannot be blamed, even when he's eight and the tiny human thrust into his arms is a brand-new, female sibling. He is still young. He still hasn't learned how dangerous these tiny humans can be. Before he can take precautions, there are somehow two tiny humans who have wormed their way into his heart, and stay there, forever and ever.

Even when one of them turns out to be so broken, that he lives in terror of what ills she can bring. Even when one of them is determined to destroy himself, bit by bit, and needs his brother to rescue him from the swamps of addiction, again and again and again. They are still there, in a heart now frozen over.

Mycroft Holmes doesn't trust babies.