Radiographer, here. Yes, that’s called a Pigg-o-Stat (I know, weird name). You do this because it restricts limb movement and allows you to take images more cleanly. The last thing you want to do to babies is irradiate them too much, because radiation harshly affects cells that are dividing more rapidly (such as the type in growing children). The alternative is putting a lead apron on a parent and having them restrain the child, which could result in motion and thus a bed to retake the x-ray. It looks weird, but it’s quite effective.