The letter people imagine writing is a summary of everything they have learned. It is the hardest thing to write and the least interesting thing to receive.

The letters that get read repeatedly are smaller than that. They contain specifics: who you were at their age, what you got wrong, what you noticed about them. Advice, if any, arrives in passing rather than as the point.

Write to one grandchild, by name

Not “to my grandchildren”. To Ellie.

A letter addressed to a group is written to nobody, and it shows immediately in the prose: it becomes general, careful and slightly formal. A letter to one person can say “you were four when you decided you hated the sea”, which is the sort of line that gets kept.

If you have five grandchildren, write five letters. They will be shorter than the one long one you were planning, and each will be worth more than it.

You can still write a single piece for the whole family. That is a different document, and it belongs in your life story rather than in a letter.

What actually belongs in it

Who you were at their age. Not who you became. What you were like at nineteen, including the parts that do not reflect well. This is the single most-read thing in any letter of this kind, because it is the one thing a grandchild cannot get from anywhere else and cannot picture on their own.

What you got wrong, specifically. Not “I made mistakes”. The actual mistake, and what it cost. A named error is useful to somebody. A general admission of imperfection is not.

What you noticed about them. Something particular you saw in them that they may not know you saw. This is the sentence people go back to.

What you did not expect. Something about your own life that surprised you. Where you ended up living. Who turned out to matter. What stopped being important.

One ordinary day, described properly. A Tuesday from your thirties, in detail. Ordinary days vanish completely from family memory and they are what a life is mostly made of.

Something you want them to have, and why. A book, an object, a place worth going to. The reason matters more than the thing.

What to leave out

Instructions about how to live. A letter that tells somebody what to do is read once. A letter that tells them what happened to you is read many times, and it contains the same advice in a form they can use.

A résumé. Where you worked, in order, with dates, belongs in a document rather than a letter. Nobody has ever reread a career summary.

Grievances about people who are still alive, and particularly about their parents. This is the fastest way to make a letter unusable, because whoever receives it will feel they have been handed a weapon.

Anything you would not say to their face. A letter is not a chance to have the last word from a safe distance. If it would be unfair to answer, it is unfair to send.

Predictions about the future. They date badly and they make a letter feel like a period piece rather than a voice.

Say plainly that you love them

Write it. Do not imply it, and do not assume it is understood.

Many people of a generation raised not to say this find it excruciating, and write around it for three pages. The grandchild reading it will look for the sentence, and if it is not there, they will wonder.

One line is enough. It does not need to be elaborate and it is better if it is not.

Length and form

One to three pages. Long enough to say something, short enough to be read at a sitting and reread on a bad day.

By hand, if you can. Handwriting carries the person. A grandchild holding a page in their grandmother’s hand is having an experience that no typed version reproduces, and it is the part people describe as unexpectedly affecting. If holding a pen is difficult, that is worth solving rather than accepting: helping an older parent write by hand applies just as well to yourself.

Date it, and say where you are. “Written at the kitchen table in Hebden Bridge, 4 October 2026.” That single line places the whole letter in time, which matters enormously to somebody reading it thirty years later.

Do not write a final draft first. Write it badly once, then copy it out. Trying to produce a fair copy at the first attempt is why so many of these letters get abandoned halfway down page one.

When it should be read

Two schools, and both are defensible.

Give it now. They get to say something back, ask what you meant, and thank you. You get to know it landed. The letter becomes part of a relationship rather than an artefact of one.

Leave it to be found. It arrives when it is most needed, and it carries a particular weight for that. It also removes the awkwardness some people feel about being thanked for something sincere.

If you leave it, make sure somebody knows it exists and where. Sealed letters get lost in house clearances more often than families like to think. Tell one reliable person, keep it with important documents rather than in a drawer, and label the envelope clearly.

The middle option works well for many people: give a letter now, and keep writing others.

Write more than one, over years

The strongest version of this is not one perfect letter. It is a short letter every year or two, each one dated.

The set is worth more than any single letter, because it shows change: you at seventy, you at seventy-eight, the same person thinking differently. And it removes the pressure of the definitive statement, which is exactly the pressure that stops people writing at all.

It also means the first one does not have to be good. It only has to exist.

If you cannot start

Answer one question instead of writing a letter.

“What were you like at twenty?” Write the answer. That is most of a letter, and you can put “Dear Ellie” at the top afterwards.

The blank page is nearly always the obstacle, not the affection and not the material. Give yourself a question and the letter tends to write itself, which is the same principle behind every guided journal that has ever worked.