How to re-acclimate my cats with my kid?

Your best option is to limit the places they have to hide- close a few doors and try and keep them in a central area. Have your son sit very still, and have him offer them a treat they enjoy- or sit near your son and offer the same, as they may trust you more. It will take time and he will need to be quiet and still so you may need to do this many times (if he gets bored and figets it's time for a break)