it really depends on your children, and how much time they spend in england. i would recommend you send them to boarding school there until they’re about 15 – 17. which should allow the accent to become their ‘default’ but unless they make a conscious decision to maintain it, it will likely slip gradually.
i’ve spent most of my life traveling (and still do), so i have an accent that’s a bit of a mixture of british and australian. i try to keep it as neutral as possible by deliberately not using words/habits overly associated to either. americans often ask if i grew up in the uk, and brits sometimes think i sound a little american.
accents can be tricky, i have friends who can ‘switch’ between them at will, but i have difficulty doing that. i tend i adapt to who i’m talking to subconsciously.