I’d send cards and small presents, so that the children know they’re in your thoughts. I hope your problems are just temporary.
For those with long estrangements, Septimia’s suggestion of writing
a letter for grandchildren to receive later, with family history/stories in, is an excellent one. I’m (slowly) filling in a Grandparents’ Journal in triplicate for my AC to pass to their children, though thank God there’s no estrangement involved.
I never knew anything about my maternal grandparents. My mother didn’t talk about them and I never saw a single photo of them or their own families. Of course it’s easy enough to find out names and dates of our ancestors these days, but there’s a great big black hole in our family knowledge, and that of my children, grandchildren, etc, that can never now be filled in. You know when you find yourself wondering who a child looks like, or where that particular habit or look came from? Simple things, but important.