Don't wake up the sleeping child.

Source: Tatoeba

The baby seemed to be sleeping a sound sleep.

The baby seemed to be fast asleep.

The baby seemed to be in a deep sleep.

Source: Tatoeba

There are mothers and fathers who will lie awake after the children fall asleep and wonder how they'll make the mortgage, or pay their doctor's bills, or save enough for their child's college education.

Source: Tatoeba

The baby was sound asleep in her mother's arms.

Source: Tatoeba