I found it hard work. My granddaughters, when they were about 12 and 10, used to 'help' me. I let them have a little stall of their own where they sold old toys and books, and it was fun but chaos!. Every time they sold anything they tore around with the money finding more things to buy. And bought endless ice creams and sweets etc. I hardly sold anything as I was so busy trying to keep track of them.
I didn't do many of these boot sales as it was too much like hard work for very little reward.
I don't think it matters if you park crookedly, Lizzies, but do look out for very early hunters of anything valuable etc as they do pounce incredibly quickly. I definitely feel that it's best to have someone to help.
Good luck. It can be fun. 
The far left in France, could it happen here?
What is the most random school memory you have?
. Next time I had someone there who just kept them away until I'd just finished setting up.