That's pretty pricey - almost all regular trainers are adjustable, though a 20" wheel is pretty small (I do seem to remember one of my teammates saying she put her son's little BMX in a trainer when he wanted to be like his mommy - then again I don't know if she used any resistance for a 6 yo....). I'd say take your bike to a shop and ask them to test out some trainers to see if they'll adjust enough for your wheels. They should have some floor models out and let you.