User blog comment:SayuriDarling/The House of Hades Official Discussion/@comment-19761484-20131011203358/@comment-7153535-20131011223747

In the House of Hades it said that the way the Son/Daughter of Poseidon acts is reflecting that side of Poseidon (ie. Calm and nice or stormy and unforgiving)

About the undead thing the answer is no, unless you are talking about a one-ish year old baby because the Big Three were under oath not to have kids until Percy asked that to end in TLO