My kids are all in elementary school by now, but I’ve only ever spoken English with them, and my husband has only ever spoken Japanese with them.
It was a bit of a journey in our case, as we were transfered to Australia for three years when my kids were aged 3, 1, and 1. They quickly took on English as their main first language in that time, even with the one-parent-one-language strategy, and while attending Japanese school once a week.
Coming back to Japan, they spoke very little Japanese at first, but became as fluent as their peers within a very short time, a few months at most. My oldest is now fully bilingual, due to getting proper school exposure overseas, but my twins speak Japanese 90% of the time, due to coming back to Japan at pre-school age. They usually speak to me in Japanese even though I only speak English to them. They do understand 100% of what I say though. We send them to English saturday school, and do movies, books, apps in English too.
I did see some comments above worrying whether two languages will cause speech problems. I had this worry before, but was told by a very senoir pediatrician to definitely continue with bilingual exposure as much as possible. So, on we go 🙂