The exit of saliva from the mouth of the child is the result of two types of increased saliva:~
The first is excessive false saliva, meaning that the salivary glands do not secrete an excess of saliva, but the child does not swallow saliva in an adequate amount equivalent to the amount secreted from it in the mouth (decrease clearance), as well as his inability to control the muscles of chewing and expression surrounding the child’s mouth, so saliva escapes and flows from his mouth.
The second: which is the real increase in saliva
And it occurs as a result of excessive movement of the muscles of chewing and mouth, licking and sucking his fingers and things in the house, which excite the nerves and the salivary glands attached to them, and therefore saliva is secreted in a large amount that flows from his mouth.
Also, when inflammation and infection occur, excessive salivation occurs
As an accidental result, such as infections of the tonsils and mouth.
Or when the teeth appear, a wound occurs, and it stimulates the secretion of saliva abundantly as a physiological result to accelerate the healing of wounds, because the saliva carries (growth factors) special and non-private healing and immunity factors, and this is a blessing from God, the Mighty, the Merciful, for the healing of oral and pharynx wounds.

Dr. Ali Abdul Hur Al-Ibrahimi
College of Dentistry/University of Karbala