I spent one christmas in Istanbul 10 years ago, it is nice but it was very cold 🥶🥶🥶❄️❄️❄️. Especially the Bosporus boat trip i swear my toes freezed hahaha. But the vibe matches the holidays especially when its snowing . Hope one day you get to visit it too. I have also visited Antalya which is a top family attraction with the sea and all the family resorts there.