Actually, the trampoline we are getting has pads over the springs and frame as well as a surrounding net. You can see it on the link below. My kids use it at school, but that is here in Singapore and we are moving to London where they won't have it. I have never liked trampolines until I saw these ones. As a responsible parent, I would also stipulate one child on the trampoline at a time, but the teachers at school have also drummed this into them.
my son jumped on a trampoline last year and was unable to walk later that day. I had to carry him from a friends house to the car. He was fine the next day, but I won't let him on one again. I then found the attached file.
He has not experienced problems in a bouncie, maybe because they are more firm? So, these, i still let him enjoy.
On page 8 of the attached PDF:
Fun but not recommended
Safety –fracture risk
Ok to sit and be bounced but not ok to stand and jump
Risk of myoglobinurea caused by working the muscles too much which can lead to kidney damage (coca cola/dark coloured wee)