There are 2 waysIf they are in USA on different visa, You can apply by using i-539 form. Check Application To Extend/Change Nonimmigrant StatusIf they are not in USA. Your spouse + your son can attend Visa interview for H4, dependent Visa based on your h1b petition, your supporting documents + their passports etc.,If you still need any further guidance, please feel free to drop an email to sharinginfoashelp@gmail.com