If it makes it any easier I run an old, steel-framed fixie, an alloy/carbon road bike on 10-speed Veloce componentry with Campag Sciroccos and a slightly tired Pace rc303 hardtail.
If you want Boris-style bikes, any of the above qualify.
As a young child, I ran a blue and red tricycle with direct drive to the front wheel. This may be harder to source in adult sizes.
I hope I have helped but I fear that perhaps I have not.
