Why not speak to them in both? If they're near adulthood already it might be too late, but if they're young kids are basically sponges for languages. And growing up bilingual makes it much, much easier for them to learn a third language down the line if they ever want to.
Speaking to them in your native tongue isn't going to make them worse at English if they're growing up in an English-speaking environment.
My father's parents were immigrants and they spoke their native language to each other, but they didn't want their kids to learn it. I've tested my father and he has about a 5000 word vocabulary, pretty good for someone whose parents didn't want him to learn it!
Kids have an incredible ability to learn languages, given motivation, and they don't need to go to school to learn words like "accountant" reading books will do.
The reasons are non-linguistic - I emigrated partly to get away from the culture of my birth. I want to heavily curate my kids’ experience of that culture and teaching them the language isn’t going to help that.
To me, giving your children a second language is an incredible gift. Setting the pathways in the brain that separate concepts from the written and spoken representation, the abstractions of different grammars, etc, is very valuable. And something that I have really valued as I grew older.
But I (superficially, of course) understand perhaps why you'd like curate their experience of something you took fairly extreme steps to escape. That might well be the greater gift.
Appreciate your perspective -- thanks for sharing.
