@Bella Dea,
Wingnuts are a safety hazard; littlie can trip and bang head.
Actually, any nuts/bolts are a safety hazard unless they're countersunk. (See how playground equipment is made.)
Sorry to be so late with contrary advice....
Edit: And make sure you trim the ends of the bolts, if any are exposed.
Edit Edit: I think your idea of zip ties is pretty good, actually. As long as you use four or five of the heavy-duty ones.
Edit Edit Edit: That's how some friends did it, and it works great.