This might not fit with your characterization of Mycroft, but I can sorta imagine him and Sherlock being little and being supervised by John and Papa Lestrade. What are your thoughts? Is it unrealistic or plausible?

sadieandmo:

Sadie:

Hmm…normally, I don’t see Mycroft as a bottom, let alone a Little, buuuuuuuuuuut maaaaaaaybe I could be persuaded to do a one-off ficlet. Let me stew on that for a hot minute and get back to you, anon!

Sadie:

I have NOT forgotten this, anon! I’m still stewing!