Translation:Your kids are all grown up.
"your children have all grown up" was rejected but should be accepted
I almost always translate the perfective "了" to a perfect verb conjugation when I do paid translations, especially when they're at the ends of sentences.
What's the 都 doing here? "All grown up" is a set phrase and can be used of even one single person. So it looks like they're saying "all of your children have grown up" rather than the idiomatic English "your children have fully grown up".
What do other native English and native Chinese speakers think?
"Your kids are all grown up" isn't the same as "your kids have all grown up", which is what the translation should be.
"Your children are all big now."
I think this can be accepted as both the English and Chinese versions can both mean it literally or otherwise -- usually not literally. I can imagine saying "wow your kids are big now!" to someone, when I don't mean just physical growth.
Sorry, in this context da doesn't indicate size. It simply means they've become adults [and could be very small adults potentially ]