Babies are hard, well hard. They can walk (crawl?) through all manner of chaos and calamity, through bullets and explosions, and shrug it off because they feel no pain.
Except that they do. Babies can feel pain; please for the love of God don't believe they can't.
The oddest thing about this belief is that we did initially believe (know, surely?) that babies had the capability to feel pain. Sometime in the 19th century this belief got turned on its head.
Infants were considered underdeveloped in terms of being able to distinguish pain or even understand it. This led to many simple surgeries being conducted on babies with only muscle relaxants and no anaesthesia.
The idea stemmed from pinprick studies conducted in the 1940s, where infants didn't react to being poked in the arms and legs. It was thought that it was because they felt no pain, but was actually because their limbs were underdeveloped (and, you know, new) so they didn't always have reactive capabilities.
Anaesthesia can be a rather difficult thing to administer to such a small body so in certain cases this makes a little sense. But there seems to have been a collective blindness within the whole 'babies can't feel pain' theory, which was only really disproven in the '80s. The 1980s.