In addition to what
debbie276 mentioned, it can also happen when there's not enough of a nest shape with the nesting material.
That's a common problem for hookbills, especially 'keets. Some seem to prefer a near-bare floor in the nest box.
So it's slippery, like Debbie mentioned, and it lacks the nest shape, which naturally pushes the chick's legs under their body.
I know that some use a felt pad on the bottom to solve the slippery-ness issue.
I've dealt with a juvenile who had splayed legs. It was sun conure and she was much older. I got her around 6 or 8 weeks, if I recall?
I tried using a sponge, but she kept biting at it and I was afraid she'd eat it. So I had to use the fabric tape instead.
I imagine you won't have any trouble with the makeup sponge as long as he's super young. They're not mouthy until they're older. But I'd keep an eye on the parents. If you see any missing sponge bits, you might want to switch to another method.
My results weren't that good because of the bird's age. The bones, muscles, ligaments, etc. were more fully formed since she was a bit older when I got her.
We got the legs to go in somewhat - enough to be totally functional. But it wasn't a normal stance by any means.
But with the young ones, I know you can get really good results since they're still growing and the bones aren't fully matured yet.
I'd just make sure he's propped up and positioned in a way so that he doesn't tip over and end up stuck on his side.
The sponge method doesn't allow for much movement at all, so you can end up with a situation where the baby falls over and they get stuck on their side. I imagine it would be uncomfortable, but it could also prevent him from eating properly.
So I'd peek in to ensure he's upright.
If he's tipping over and getting stuck on his side, there's another method where you make something that looks like a baby walker (only it's stationary.) So they sit in a little cradle (for larger birds, some people use a canary nests, with two leg holes cut in the bottom.) and it's propped upright.
the other two are fine. I googled and found many videos on how to deal with splayed legs. I watched one video where the guy used nylon ties one on each leg and one connecting the two legs then watched one where they used foam makeup pads. I chose to use the foam pads as they would not irritate the babies legs. Followed instructions and got the baby all set up and will check it as often as I can so as not to disturb mom and dad feeding them to much. All the chicks are well fed with full crops. 
that this little one makes it.
