We are in the market for a trampoline for our two boys aged three and five years. Does anyone have a trampoline and can give me some advice?

I had one when I was a child but not until I was 10 or so. It was a huge rectangular one with no safety attachments.

Now there are circular ones for sale as well as rectangular ones. The circular ones have safety nets on them. Is having a safety net a bit OTT? Shouldn't we let our kids understand danger and their limitations and let them learn to be careful? Or should we provide them with extra safety if it is available? 

And to the important question. Can you do a somersault on a circular trampoline or not? Is a rectangular one better?! 

Growing up we had a round one and so that is all I know, we did plenty of somersaults and such on them without a problem although perhaps it's easier on a rectangular one.  I have 4 little girls agest 2-7 and we bought a round trampoline last year, we do not have padding on the edge nor do we have the enclosure and we have not had anybody get hurt, like you said I think they need to know their limitations and such.  I do think inevitably somebody is going to get hurt, it's just the nature of children and things that propel them in the air:) but we are loving our trampoline and I do not feel like we need the enclosure.  Hope that helps