Trek Mountain Train tag-a-long kids bike (Williamson Park LA1)

Trek Mountain Train 206 kids tag-a-long bike.
20" wheels and 6 gears
Attaches to seat post of the adult's bike via a collar which is designed to allow some articulation.
(The collar is only suitable for one size of seat post. I think the bike would be supplied with three as new, but others could be obtained I guess. Or could perhaps adapt it if you're clever enough.)

I'm guessing it would suit child of 5-9 (up to 36KG)
Similar to this - https://www.trekbikes.com/gb/en_GB/bikes/kids-bikes/mountain-train-206/p/15...

It looks like the instructions are no longer available online but see these that have been archived at archive.org for riding and connection guidance...
https://web.archive.org/web/20101116203718/ http://bike-manual.com/brands/trek/om/trailerbike/index.html
https://web.archive.org/web/20090405131508if_/ http://www.bike-manual.com/brands/trek/om/trailerbike/trbike_hitch.html
https://web.archive.org/web/20090405184649if_/ http://www.bike-manual.com/brands/trek/om/trailerbike/trbike_conn.html

It's been stored outside under cover, so has acquired some rust marks and will need oiling, etc.
The gears work but are a bit stiff. The tyre will need at least pumping up.