I'm fully Greek and my son is British. We came back in Greece for a long stay, until end of October. My son's 90 days are up 3rd of June. We do have an appointment at the Special Registry of Athens(only place to register births outside of Greece) end of July, and subsequently we will apply for a Greek passport. By that time he will be an overstayer.
What do I do? Do I go back to the UK and apply for citizenship through an embassy or overstay and apply from here? In the latter case, are there any legal implications?
Edit: my son is 4 months old. I am the father. Both me and the mother are fully Greeks and were legally married at the time of birth. Our son had the right for British citizenship due to us being permanent residents in the UK.