In reply to beardy mike:
I've never bough a new bike for my 3 kids, always second hand. 12",14 and 16" wheel bikes all came from the local community recycling centre and cost less than a tenner each. Moving up to 20" was a bit more expensive but I found a Specialised Hotrock 20 at a local bike charity for £14, to be fair it needed a new saddle, drivetrain and breaks, but was still a bargain compares to a new one at around £200. When the kids were big enough for a 24" wheel I found the local secondhand market was full of barely ridden Hotrock 24s for only £40! (£260 new)
When they eldest outgrew the 24" wheeled bike I started scouring the local second hand ads for a 26" frame in extra-small.. 3 years later I found a Kona Fire mountain which went to kid number 2 as in the meantime eldest was tall enough for a small. The middle kid has outgrown eldest kid and is now eyeing up my bike.
I found the 24" and 26" bikes on Gumtree the furthest I had to drive was 35miles.
XS 26" frames are like hens teeth, 26" MTBs have been obsolete for nearly ten years, every keen cyclist in the country is looking for them to build a fancy bike for their kids.