بسم الله الرحمن الرحيم
Ulama have explained if zakah is given to a person thinking him eligible for zakah or non-Sayyid on the basis of some reasons then zakah will be paid though it is known later that the person was not eligible to receive zakah or he was a Sayyid; since you have given zakah to those orphans and on the request of their mother thinking them non-Sayyid, hence your zakah was paid as per the Shariah, though you learnt later that they were Sayyid. You should not worry about it, but be cautious in future.
دفع بتحرِ لمن ظنه مصرفاً فبان ….. غناه …أو أنه ….هاشمي لا يعيد؛ لأنه أتى بما وسعه الخ (در مختار مع الشامى 3/302، ط: زكريا)
Allah knows Best!
Darul Uloom Deoband