I love my children but I rarely tell them or show affection openly. Is expressing love out loud a cultural extra, or is it part of the Sunnah?
This happens in a great many homes. The love is fully there, but it stays inside. In the houses most of us grew up in, affection was shown by working, providing and protecting rather than by saying it out loud. That is a habit, not a fault, and a habit can be opened.
Now to the question itself. Saying love out loud is not a cultural extra or a modern softness. The Prophet, may Allah bless him and give him peace, instructed it plainly.
“When a man loves his brother, let him tell him that he loves him.”
The Prophet (peace be upon him), Sunan Abu Dawud (5124) · meaning
If we are told to voice our love even to a brother in faith, then children whose whole world is your face and your voice have more right to hear it, not less. Love left unspoken warms your own heart. Love spoken warms theirs, and it is theirs we are raising.
He did not only say it, he showed it openly. He was kissing his grandson al-Hasan when a man sitting with him said that he had ten children and had never kissed a single one of them. The Prophet, peace be upon him, answered:
“Whoever does not show mercy will not be shown mercy.”
The Prophet (peace be upon him), Sahih al-Bukhari (5997) · meaning
Hold that scene in view. The most dignified man ever to walk the earth kissed a small child in front of others, unhurried and unembarrassed. Letting tenderness be seen was not beneath him, so it cannot be beneath us.
The effect also reaches past the moment. A child who hears the words and feels an open embrace grows up with a settled sense of his own worth, and later says those words easily to his own children. What you speak today travels on to people you will never meet.
So do not wait for an occasion or for the right phrasing. Say it simply, in your own words, in your own voice. Love that is already this full in the heart has only a short distance to travel to the tongue.
One small step: Today, look one of your children in the eyes, put a hand on their head or shoulder, and say the plain words out loud: “I love you.” Once is enough. Tomorrow it will come easier.