Your son may not be comfortable with his outfit. Sweats at during sleep would occur especially if he is wearing a thick and not breathable clothing. Why don't you give him a baby sleep sack that would fit nicely on him. Sleep sacks are wearable which provides a comfortable feeling due to its breathable and sleeveless design. Also, I advice you not to feed him excessively before sleep because it could be unhealthy. Water or milk is should be fed moderately.