You should file for custody of the minor child under the Guardians and Wards Act on the ground the best welfare of your school going child is to be in your custody as you can not only financially afford for his education but even see that his studies do not get affected by the wrongful acts of your wife by filling false criminal charges against you.
The wife can get visitation right for which you can always agree as she is the biological natural parent like you but by keeping the child exclusively with her in an atmosphere where she herself being misguided by the relatives for going ahead with unnecessary false and malicious prosecution will be bad for the mental health of the child too at the growing age.