Our son was diagnosed with Autism and ADHD this year. Is he considered disable due to this diagnosis?

If the child is under the age of 13 there is no benefit for indicating they are disabled.

This is the IRS definition of permanently and totally disabled -

Permanently and totally disabled. Your child is permanently and totally disabled if both of the following apply.
• Your child can't engage in any substantial gainful activity because of a physical or mental condition.
• A doctor determines the condition has lasted or can be expected to last continuously for at least a year or can lead to death.

If your son is an age to qualify as your dependent, then he would not be eligible for any additional credits due to disability. However, if he is otherwise qualified but past the age for the credit, then if he is permanently and totally disabled, he may continue to qualify for credits. 

The IRS states:
 A person has a permanent and total disability if both of the following apply:

• They can’t engage in any substantial gainful activity because of a physical or mental condition and
• A doctor determines their condition:
  • Has lasted continuously for at least a year or
  • Will last continuously for at least a year or
  • Can lead to death
     

You can use the IRS self-help tool to see if your son might qualify.