Can any one recommend an on line diary site. I want to put something together, so perhaps my children can read in later years!

If it is most important that it can be read years later, I would definitely use a paper diary.
Reason is the business continuity of any website. You wouldn't like to be dependent on that.
And then there is the privacy issue...

Agree! I spent hours of my youth constructing a website, of which today I have maybe one or two files to show of it, thanks to technology.

I started something for my daughter, inspired by watching a sad film one evening, that if I died whilst she was still small she would probably never remember me. So every now and again, I write a letter to her, to open when she's old enough to want to learn about herself. Much better than technology!

Not directly about our children as it started before they were born, but I write an annual letter which goes (these days some by email) to friends and relatives all over the world. It's quite fun reading the old ones and occasionally I want to look something up to see when it really happened.

One positive side of sending it to so many people is that I tend to get reminded that it's high time I did another by the recipients themselves who, in November, write to ensure they haven't been knocked off the list. Without the confirmation that it is appreciated and looked forward to, it might have been one of those 'good intentions' which I only kept up with for a year or so. It's forty years on now and I've only missed once.

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Longbyt

That's a very nice idea. I'm sure it will be appreciated later.

Like the others, I suggest a paper book diary.

I have the one my grandmother wrote (wasn't a diary but stuff about healing as she was a healer). It's probably 50 years old by now and I'm glad to have it.