Sherlock Holmes was, as one might assume, very inexperienced when it came to babies. When John had first posed the question of moving back in – and really it wasn't a question in Sherlock's mind – Sherlock had said yes immediately, without giving much thought to Rosamund.
He had met her, of course. Interacted with her for a few moments at a time until her dribbling and nonsensical babble proved boring. Held her until she started to cry, upon which she would promptly be returned. He didn't dislike her, but sometimes he simply forgot about her.
But now that she lived with them, everything was different. It was impossible not to be aware of her. Bottles next to beakers, toys strewn about amidst crime scene photos, diapers where lab equipment used to be. John had also become much stricter about experiments, which was terribly dull.
But there were times when little Rose baffled Sherlock in the best of ways. How effortlessly she could unlock John's softest side. How listening to her inane babble could somehow help Sherlock crack the case. How someone so small could so easily take up permanent residence in Sherlock's mind palace.
He considered all this, hands steepled under his chin as was his custom, while the baby's laughter echoed down the hall like the tinkling of the sweetest bell.