Our daughter used to sing softly at night. We thought this was fine. Success can also be rewarded by a wider range of choice for breakfast the next morning. Star charts can be utilized as well, wherein a certain number of stars for good behavior are translated into a trip to the park or other spend time together activity. Rewarding good behavior is generally more effective than punishing unwelcome behavior.
Children can awaken for other reasons.
Occasionally a child may have airway obstruction and resultant sleep apnea as the cause. Such children tend to snore, hold their breath during sleep, and are unusually drowsy during the day. Your son seems to be going to bed at an appropriate time. However, he may still need his afternoon nap. Children often do until about age four.