Can you sit down on a bmx?

Answer 1

Most will fit, but that's not the same as saying that most can be used. On a bmx you run a higher than average risk of sitting down heavily on the saddle, so you want one that can take the kind of abuse.

Answer 2

Of course you can, but as the seat is low, it's possible that you will sit on the wheel too. you mostly won't be able to pedal while sitting.