Is it harmful to let him cry to sleep?
It can be really hard to listen to your little one cry during the sleep training process. Rest assured that there is no evidence to suggest that letting him cry at bedtime as he learns to fall asleep on his own has any negative impact on his psychological well being. In fact, little ones who can fall asleep independently at bedtime and sleep well are more predictable, show secure attachment, and are less irritable. So, as long as you are giving him positive attention during the day, there is no evidence to suggest that allowing him to cry at bedtime is harmful or affects attachment.
If you do not physically go into the room to check on your little one to see if he is okay, be sure you are able to monitor him in some way (for instance, a video monitor) to make sure that he is not upset due to something like having an arm or foot stuck between the crib rails.About Dr. Sonia Rubens