The unstraightening thing is actually because of the construction of the bones. The bones bend a little, just a little, more than straight and there is a muscle

The unstraightening thing is actually because of the construction of the bones. The bones bend a little, just a little, more than straight and there is a muscle that can pull on the other side. This locks legs in place when straightened, but still maintains a spring-like mechanism protecting the weak points in the bone structure (because it's not actually straight, it makes an angle). A baby is actually too weak to hold himself up. I'm not saying that that's the only problem, but his muscles are certainly not capable of holding his body off the ground the first 2-3 months. That's why it's important to put them on their belly (but not leave them like that for more than 30 minutes or so), and ideally try to help them crawl, roll and walk, even when they can't. They'll love standing up, and hanging from the side of the cot. Plus they'll love the attention. And don't worry about babies and young kids falling over. Their skeleton can actually absorb more force than yours can (because it isn't nearly as rigid as yours, which probably also means it's much harder to walk with). In addition to that, they weigh less, and F=ma, so they can easily survive drops that would kill or severely injure an adult.