Logical Persuasion (doesn't always work)
Mycroft looked at the little, pink thing, his expression singularly unimpressed.
It was hunched and wrinkled and looked deformed. He knew little and cared even less about the new born of his species. Natural inquisitiveness had deserted him and he had spent six months cultivating a deep disinterest in babies.
"He is misshapen. When Skippy gave birth to that puppy with a broken..."
"No, darling. We are not drowning the baby."
Mycroft gave an internal sigh. Mummy was obviously going to be unreasonable about this.
...
Sherlock had food in his hair. More to the point, Sherlock had food in Mycroft's hair.
The baby poked at his food, crushed it with little fingers, squeezed it in his fist, put it in his mouth and spat it out, threw it, combed it through his hair and mashed it into any surface. Very little made it into his gullet but still Mycroft never offered his help.
"You shouldn't, mummy," he explained. "It is basic Darwinism and if one cannot feed oneself then it follows that..."
"No sweetheart, we are not starving Sherlock."
Mycroft was disappointed in Mummy. He had always thought her to be an unsentimental advocate for natural selection and survival of the fittest.
...
"Make a pile of all the things you wish to dispose of. Your things only, mind. Daddy's pipe and my travel case are off limits."
Mycroft nodded politely and spent the morning pulling out clothes he had grown out of, things he disliked and books written by people who could only hope to aspire to idiot status. He put it all into the sturdy Oxfam sack and dragged it downstairs.
In the hallway a pink-cheeked Sherlock slept in his pram.
Mycroft eyed him. And eyed his sack. Mummy had said things he wished to dispose of... If he was careful, Sherlock wouldn't even wake. Mycroft pushed the books to the bottom and made a nest out of the clothes.
This is where he made his first mistake. Thoughtless. Idiotic.
He crouched on the landing and peered through the balustrades, holding his breath as Mummy peeked into the sack.
"Mycroft!" she called.
He dragged his feet as he came downstairs.
"Yes, Mummy?"
What could possibly be the matter this time?
Oh. Of course.
He could only dispose of what was his.
"Well, he is MY brother. I should be allowed ."
He tried to keep petulance from his tone. Points of logic should be made calmy and concisely.
She smiled.
Mycroft frowned.
"I am so glad you came around. But he is mine too, and I overrule you."
Yes, this was his first mistake with Sherlock. The first time he admitted that Sherlock was his, and realised that Sherlock would use this as the thin edge of the wedge to force his way deep into all their lives.
Who would have guessed that a little thing that couldn't walk, talk or feed itself could be so brilliantly manipulative? Mycroft felt a small flame of admiration leap to life.