Depends on what kind of set-up you have. Judging by your idea, I doubt you have any contract in place with the "roller-bladers" that covers you in the event that they hurt themselves, in which case, if they do, and they push a suit on you, you could theoretically be liable.
On a side note, I had people do leaflet delivery for me, the action rate was absolutely disgusting. Common sense would've told me that of those who actually pick-up the leaflet, 95% of them will throw it away, and of the 5% who keep it in the possibility of using it at some later date, a very minimal amount will actually convert.
Alas, I busted over $800 on leaflets + delivery. I ended up having to burn over 6000 overstocked leaflets, as the cost of delivery just wasn't worth it (I was paying roughly $8 an hour).
