Well… kids at least have their sutures open for significantly more flexibility to their skeletal system. They’re less likely to get hurt in some cases, when its blunt force things… unless its like a hammer to the head, that’d inflict less damage on more solid skull of an adult.
A kid would fare better jumping off a ten foot roof, but not if they landed on their head. The biggest weakness is lack of muscle and multiple-bone-skulls that are thin that don’t protect their brain as well.
An adults muscles would also protect them to some extent. Tensing up before something disastrous is essentially protecting yourself with your muscles. Being too young could render them unable to protect their spinal cord from snapping. No musculature to make sure that it doesn’t get twisted the wrong way.
Burning… hmm… I think an adult would survive quite a bit better than a child. More body fat, and larger lungs to deal with smoke inhalation.
I probably wasn’t supposed to take this question all that seriously…