there are tiny knickers made for babies whose parents use the Elimination Communication method (instead of nappies, in effect, it's toilet training from the beginning, or early on).

i toilet trained my child when she was two, and as she was a very small two, the size 2-3 knickers in the usual shops, didn't fit her either. so i also went searching for smaller than usual, knickers.

i think the site i found most options on was tribalbaby (it's an australian EC site, with links for products, such as tiny knickers).

if you sew, Noonee Wilga's site has a pattern for sale, for making tiny knickers. Or she will make you custom tiny knickers - you just send the measurements of your child.

Training pants? They are underwear, with sew in absorbency - enough to absorb one wee.

The first time i heard about tiny knickers, was when i was pregnant, when to a meetup of mums, and met a seven month old bub, who was wearing knickers, and keeping dry (we were at that playground for three hours, each time she wanted to go, she signalled to her mum). Her mother was using the Elimination Communication method. Had never heard of it before.

Elimination Communication was not something i ended up doing, but i read that tribal baby site, and it gave me lots of tips, to toilet train my child (at two and a half).