@tinytox2 I'm so sorry that you're going through this. It changes your life, I know I'm also prevented from seeing my grandchildren by my daughter.
For those people who are sceptical about being arrested for sending a birthday card, this can happen I have myself heard of this happening to other grandparents. It's a disgrace. Although police force vary from area to area ( thankfully our local force are lovely), others are awful, much like any of all organisations, varying from area to area.
Sadly I don't think there's a lot you can do at this point, unless you have a family member prepared to do some liaising work? If not, I would definitely try to focus on yourself, put away pocket money into an account for your grandchildren so they know you are thinking of them. Build a memory box for the future.
You never know in the future you might find that the door will open again, and you will be stronger then.
You are understandably worried that your grandchildren will be missing you, sadly they may be, you just have to remember that you have tried to stay in touch & the law sadly isn't on our side.
Some of these parents have no mercy.
What I would say is that like all of us (we've all experienced loss & trials as children & adults), they will find their way. Hopefully back to you one day