Even nearly 12 years after the death of DS1, I can get floored by this question.
He died as a new baby, and the time before we had other children was both distressing and awkward. It's such a normal question, and I was stumped: if I said none, I felt terrible for abandoning DS1s very existence; if I said one, then the normal follow up questions floored both me and enquirer who, quite rightly, would expect ordinary chat.
I did try out "none" plus a muttered or silent "living", but that never felt right.
Even after the arrivals of DS2 and DD, I couldn't find the right answer: I have two children living with me now, but I am mother to three. It's a bit easier to deal some questions "two at this school", "those two over there". But there are times, even after all these years, when I just don't want to omit DS1, and it's back to unexpected answers and explanations, and dealing with enquirers' reactions.
What do others in this situation do?