Above ground pools are nice. We have had both kinds, soft side and the hard side ones that have poles.
The pro's to a soft side:
The soft side one was so very very very nice because it was, at max, 3 feet deep and 12 ft. across. I could step over the side and be pulling a child out for any reason within seconds. It was perfect for up to 4-6 kids ages 2-7. They could get wet, goof off, not have to much of a chance of drowning due to they could just stand up, pretty safe.
The cons:
You may have seen them on TV shows like Funniest Home Video's or something. They do slide over and the sides do roll up like a burrito. You can't get out if they do collapse. It happened to ours on flat ground but no one was in it. I was cleaning it and the water was swirling around to get the debris off the bottom moving so I could scoop it out. The water pressure just pushed the side over and it went a rolling across the yard. If a child had been in it they would have drowned, trapped between the layers of pool material. Like the beans inside a bean burrito.
They must be on absolutely flat ground, smoothed and pounded to being flat so the weight of the water won't cause it to cave in and allow the shape of the pool to become different.
You only get one shape, round. It can vary buy how large the top is but it's always round.
This is the one I had.
http://www.walmart.com/ip/Summer-Escapes-12-Quick-Set-Rin...
Hard sided:
Pros:
They are very nice and sturdy. The poles keep the sides up even if the bottom of the pool becomes uneven. They are fun because the ladder becomes a jumping off place. They are only a few inches above the water line so it's fun and not very dangerous.
The sides are flat/smooth and nothing can get trapped under the edge. They can be repaired quit easily. They cost a bit more but can be left up year round even in winter. Well, that won't apply to you of course...
You can always build a deck to surround at least one side of the pool too. That way you can sit above the water and oversee all the kids at the same time.
Cons:
They are taller and climbing into them for someone who has limited upper body strength is almost impossible. They are not easily accessed in an emergency so I would always want to be in the water while the kids are in it. I would make them get out each time I got out and they had to stay out until I was ready to go back in.
This is the one that a couple of my friends have and have used year after year.
http://www.walmart.com/ip/Intex-15-x-48-Metal-Frame-Above...