What's the finest readily-available way to write on paper? I'm trying to make the smallest legible lettering I can - miniature writing on normal paper or something thinner.
This is in the context of craft with kids, so I'd like something affordable, also not too complicated.  We'd like to make Lego-scale books (menus), though as that's around 1:40, clearly we're not going to get normal type sizes.  Colours would be a significant bonus.
The best I've done so far is with a 0.5 mm mechanical pencil (the finest I have to hand) and very light pressure - that gets me down to letters 1 mm high and 0.5 mm wide, limited by the stroke width as much as my skill. H- and F-grade pencils are similar even if sharpened with a scalpel. I've tried rubbing the pencil to a sharp point but that didn't help much.  You wouldn't fit many words on a page of say 10 mm high.
I doubt my skill is up to single-hair painting, but can't think of anywhere in between.  And yes, inkjet-printing is another option; we'll probably do some of that too.
The smallest pen I have personally found is a 0.03 mm size pen; while it does leave a very small line, the tip is quite fragile and tends to break more often than my larger pens (including the 0.05, the next size up). It requires a delicate touch; while you would probably be fine with it, I wouldn't recommend handing it to kids, who haven't always developed the motor skills to be gentle with the pen.
The 0.03 size is also fairly uncommon; typically, the smallest pen tips you'll find will be either 0.05 or 0.1. You can see a comparison of the line sizes in this sample image from JetPens, found in their product listings for Copic Multiliners, one of the brands that does carry this size of pen; Marvy and Deleter also sell a pen in this size. The image below is an actual sample of the pens, on an undisclosed lettering paper, to show comparative line weight and bleed between sizes.