When my daughter was about the age of your older kids, she helped me set up our tent. I think you should practice, practice, practice. All the kids could have a role, even the youngest, such as "hand so-and-so the hammer, please."
Once you've set it up a few times, maybe try assigning each child a "job". This one is in charge of putting the poles together, while another helps you stake it down, etc. I'd even go so far as making up names for each job, and calling the child assigned to that job by that name!
I'd also make it into a challenge to make it fun for the kids. After you've become familiar with set-up, start a timer and see if you can beat your best time!
All great ideas! Maybe the 2 year old could be in charge of stakes instead of the hammer. I don't think putting a hammer into his hand is a good idea, LOL!! Although it would definitely make things interesting!!