Hi ElectraTzitzikosta, I am an OT trained in USA and have been working in Canada for sometime. I just searched OT in Greece and your post popped up. It'd be cool to connect.
Regarding your question: A lot of times OT students/grads gain this clarity about their area of practice during their placements/internship. Are ya planning to try placements in Nicu and or in EI? Regarding doctorate in USA, it might be best to reach out to American Occupational Therapy Association (AOTA) and National Board for Occupational Therapy (NBCOT)- licensing body. Hope this helps to get you started. Look forward to hearing from you! Cheers, Shubhi