Disclaimer: I own neither the characters nor even the ficverse.

I have no idea how this plotbunny got to me, since it obviously meant to find Manzanita, but it Would Not leave me alone.
I would say this belongs either between Chapters 4 and 5 or somewhere near the end of Chapter 9 of 'Little Kid.'

As per usual, anonymous reviews get answered in my profile.

With Ran safely distracted cleaning up the aftermath of his sudden interest in baking cookies, Arthur slipped into the room he now shared with his 'twin', curious to see what might be so important that he would be needed to run interference. Conan barely noticed his return, too busy snapping at whoever was on the other end of the phone connection.

"Yes, this is important! You slip up enough with me, if you start doing it with him too then the girls are going to figure it out in half a second!"

Arthur cocked an eyebrow, amused, as Conan paced urgent arcs across the floor, practically yelling into the earring-cum-cell-phone, barely keeping it quiet enough to not attract attention.

"No you don't have to pretend you knew about him, just don't start insisting he can't possibly be genuine, that's all. And get his name right!" Conan stopped, glaring heatedly at the disguised phone in his hand as though the person on the other end could feel it.

"No. Do not come over here. If They know about us already we're screwed and you wouldn't be able to help. If They don't, then you'd only attract more attention, which none of us need."

A few moments of silence, and the shrunken detective almost exploded before reigning in his fury under tight control. Arthur was almost surprised the other boy wasn't vibrating.

"NO. Do NOT, under any circumstances, go off chasing them on your own! If they realize you know then you'll be in danger, and we're in too much of a mess to help you right now!" A beat, and Conan growled, obviously cutting the other person off. "Heiji. NO. We are NOT getting a Doyle!"

There may have been more to the conversation, but if so the former kaitou missed it, too busy cracking up so hard he fell off the bed.

Because we know what happens when people poke into the Org's affairs, and you just know Heiji would try to join them afterward. There's only two choices left for his name, and he's definitely not a Sir...
Conan's already grumpy enough about his new sibling. Triplets Arthur, Conan, and Doyle would be a dead giveaway that something's up.

This scene has been declared canon for 'Little Kid' by Manzanita, or at least her plotbunnies. (grins)