Not exactly a promo code, but this just came in...
https://en.aegeanair.com/flight-deal.../family-offer/
Children get 100% discount on the family fare and 50% on comfort flex, everyone gets 2x miles.
(this exact promotion happened pretty much exactly during the same dates last year too and, also like last year, it is valid for bookings until the end of next summer)

Edit: They've officially outdone themselves...!

or even....