Why do I have to give up custody of my child if the guardian has a power of attorney?

Hello -  I am a Maryland barred attorney familiar with powers of attorney.  A power of attorney is a legal document that generally gives another person the authority to manage your finances and make certain decisions in your stead.  It is not used to deal with legal or physical custody of a child.   The school board cannot dictate who must have custody of a child, although they may possibly have rules about enrolling children only when a parent or legal guardian lives in that school district.

Your question does not seem to be a business law issue but rather one about child custody and education law - it seems to be misfiled in a business law category.  You may want to contact a family law attorney licensed in both MD and VA as soon as possible.  There are some resources available to people who want to represent themselves pro se (without an attorney) in family law or custody matters - I do not know what county you live in, but you may want to call the circuit court for your county and ask for information on the local pro se or self help center.  Note that I do not practice family or education law, but I hope that this response helps point you in the right direction.