Regarding H4 Visa approvals

Hell Friends, I have a question regarding my family H4 Visa.

Take an example: If you applied for your H1-B Visa Extension along for you and your family, and your H1-B Visa is approved, and after some time say that H-4 visas are also approved for your family.

In this case, If we change the employer while your family is living in USA, do the H4 family members also need to re-apply with the new employer or not required, since their H4 visa is approved with previous employer.

Any information is highly appreciated, many thanks in advance.