Despite our desire to help our babies sleep, what we want most is for them to be safe. We all want to help soothe the crying baby in the first picture, and help her achieve the serenity she appears to have in the second picture. How do we do that without constricting the chest, improperly positioning the hips, or endangering her if she happens to roll onto her stomach?
The link will take you to the American Academy of Pediatrics website "healthychildren.org". To summarize the points briefly:
1. Safe swaddling snuggles the arms, not the legs. The legs should be wrapped loosely enough to be in a flexed posture, allowing proper development of the hip joints.
2. Safe swaddling is loose enough to allow an adult's hand to fit between the blanket and the baby.
3. Safe swaddling is only OK until age 2 months. After that the baby may be able to flip onto his stomach and needs his arms free to be able to safely do that.
4. Safe swaddling does not overheat a baby. If she is sweating a lot the baby may be too warm.
5. Safe swaddling is done with the baby alone in her own crib or bassinet, with no soft bedding/toys/wedges/bumper pads/pillows.
HealthyChildren.org - Swaddling: Is it Safe?