Miria has pink hair and Carlos had blonde hair, but the kid has black hair, just like Harry's black hair preceding his transformation into the demon lord.
Mia's pregnancy by Carlos either ended up being aborted due to all the violence she suffered what with being constantly raped or the baby was eaten by the demons.
I mean... yeah. You really think Harry was going to the kid of Miria/Carlos live in his mental state? Presuming it even got the chance to be born, which is a bit ambiguous at the end of part 1