Hi,
Thank you for posting in Symantec community.
I would be glad to answer your query.
Could you please provide the reason why you need additional SEPM's at three more sites.
A majority of small and medium-sized organizations need only a single site to centrally manage network security. Since each site has only one database, all data is centrally located.
Even a large organization with a single geographic location and fewer than 45-50,000 clients typically only needs one site. But for the organizations that are too complex to manage centrally, you should use a distributed management architecture with multiple sites.
Refer this article: Determining how many sites you need
http://www.symantec.com/docs/HOWTO55399
There is no such concept of child SEPM like Child DC (ADC) .
You can configure and managed domain accounts differently.
Refer this article: Managing domains and administrator accounts
http://www.symantec.com/docs/HOWTO55094