My eight years old son he lost his front two dent...

What are the reasons for the delay of the permanent teeth in your son?
Genes can affect the time a child starts having permanent teeth.
If you got permanent teeth than your peers, your child probably does.
Malnourished children get permanent teeth after healthy babies
Body size can affect the appearance of teeth. larger babies tend to have their permanent teeth earlier than little children. Babies who were born prematurely or who were very small during pregnancy are more likely to get their permanent teeth later than other children of their age.
In rare cases, a delayed appearance of the teeth could be an early sign that a child is sick. Since hormones play an important role in tooth development, delayed tooth development could be a sign of a problem with the pituitary or thyroid gland.
A delayed appearance of permanent teeth can also be a symptom of a malformed jaw
Mineral deficiency.
How to treat delayed appearance of permanent teeth?
Multivitamins
Iron
Give the child a diet rich in calcium, such as eggs and cheese
Give the child vitamin D.
Various proper nutrition
psychological support
What do I advise in the case of your son?
I recommend consulting a dentist, doing an examination of his teeth, doing an examination of the glands, examining calcium and vitamin D, and treating the underlying cause of the delayed appearance of the teeth