I would write two - one that you send to the LA and one that you don't.
My son's BM wrote a v emotional letter (going on about how much she missed him, loved him, 'till they meet again) and the SWs came down hard on her - I had to fight to be given a copy. And I understood why she wrote it and I understood why the SWs were reluctant to pass it on. So if you find yourself writing that sort of letter - maybe write it but don't send it. And if you meet your child again - then maybe when he is an adult you can show it. (The SWs were nervous about me having it in the house which I thought was an over reaction.)
So pointers. In my LA, it is meant to be written to the adoptive parents, not the child (although I am not offended if it is written to the child, some SWs (like mine!) don't like it being written to the child).
Try and say what you have been doing. It's hard - but maybe you have redecorated your home? Or got a dog? Or taken up a new hobby? Or how your job is going
- if you have a job?Something "soft" to let your child and adoptive parents know that you are getting on with your life, however painful it might all be for you. Perhaps a new cousin has been born. Perhaps you managed to take a holiday.
Or if you can - maybe a memory you have of your own childhood at a similar age? (Perhaps you liked going to the seaside at your son's age and collecting shells? Or perhaps you liked painting?) I know it sounds innocuous and trivial - but I know so little about my son's birth family and I would love him to know more.
Personally, I think it is fine to say you think of him, and love him - but keep it short. Don't let it be a whole letter about how you miss him as the SWs will likely ask you to re-write. He wants to know you are ok - as do the adoptive parents.
I find it so sad thinking about the birth family and would love to share something positive about birth family with my son - rather than a whole letter about how he is missed and how she regrets it every single day. I understand that my DS's birth mum has regrets but DS doesn't understand that and I expect won't for several years.
The letters are a bit superficial but they are so important. I finally got one 3 months after I was meant to and I was very happy to get it. It will be hard writing it but don't give up on it. Write something. Even if only a paragraph.